The link connecting the Blayneys of London with the Blayneys of Montgomeryshire, Wales
My own line, descended from Thomas Blayney and Priscilla Sargeant in London has always hit a brick wall, but information from Robert Blayney links in with "on the ground" research by Terry Muff  and Kevin McKenzie , , supported by material from William Barker's "Families of Montgomeryshire" CD-Rom , clarifies the situation.
Somewhat like the steady move of Blayneys from Montgomeryshire into Shropshire (Salop) during the 1700s - (see
Shropshire Blayneys), there appears to have been a similar 18th century move of Blayneys into the Greater London area after some initial "to-ing and fro-ing" of Thomas ap Morus Blayney [Attorney to his distant cousin Sir Edward Herbert of Chirbury/Cherbury] and the marriage of James Blayney (ap Thomas) into the Loftus family (with close royal links) during the 17th century. Richard, the oldest son of James returned to Montgomeryshire as a significant property owner and married (1st) Ann Hodson, who came from a family of haberdashers and shoe makers. Their first son, for some reason [see Comment 1], became a wheelwright and his youngest brother (Edward), a shoemaker. Edward's youngest son, Richard, became a haberdasher and wharehouseman in London, while Edward's oldest son was the Rev Richard Blayney, in turn father of a haberdasher named Richard in London by the early 19thC. Blayney numbers in London increased significantly during the 19th and 20th centuries as demonstrated by the following distribution maps:
1881 - click to enlarge
1981 - click to enlarge
My Blayney ancestors came from London and there has previously been insufficient evidence to make a definite link back to the Montgomeryshire Blayneys arising from the first Blayney, Evan Blayney.
It is now established "beyond reasonable doubt" that our ancestor Thomas BLAYNEY (tailor of London) was the Thomas BLAYNEY (b.1754 Haberdasher), son of Richard BLAYNEY, Haberdasher (born c.1726 in Montgomeryshire, who moved to London before 1758), in turn son of Thomas BLAYNEY (born c.1685±10yr Llanllwchaiarn, near Newtown, Montgomeryshire, wheelwright d.1761 Llanllwchaiarn).
In co-operation with Kevin McKenzie and Terry Muff and after considerable research into 16th & 17th century Welsh genealogies, records and papers, it is now also possible to make a very reliable connection between Thomas the WheelWright and Evan BLAYNEY, the first of that name, and then back to Brochfael Ysgythrog and other early British kings. The patronymic (patrilineal) name is thus:
Thomas (tailor of London) ap Thomas ap Richard ap Thomas ap Richard ap James ap Thomas ap Morris ap Thomas ap Ieuan Llwyd ap Gruffudd ap Ievan (Evan) Blayney.
Newly established descent from
Thomas BLAYNEY (wheelwright of Llanllwchaiarn died 1761)
to my known ancestor
Thomas BLAYNEY (tailor of London, b.1754)
1 Thomas BLAYNEY (Blaeney) bpt.1668 (Bettws Cedewain)
subsequently moving to Llanllwchaiarn.
Occ. wheelwright of Llanllwchaiarn; d.1761 
Son of Richard BLAYNEY of Bettws Cedewain and Ann HODSON.
It was probably an inheritance from Ann's father, John Hodson,
yeoman of Llanllwchaiarn, which resulted in the move to
Llanllwchaiarn by Thomas.
He was possibly a non conformist (note subsequent Roman Catholic
connections in his c17th line) and so his children may have been
baptised privately or even at a London church 
+(1)Jane/Jana EVANS m.24Feb1701 (Bettws) 
Probably a widow  so unknown maiden name.
+(2)Anne (Ann/Anna) Jones 
m.1June1717 (Bettws); bur.23Jan1732 (Tregynon)
Second wife of Thomas of Llanllwchaiarn
Ten children: Thomas, Richard (x2), Margery, Elizabeth, Ann,
Mary, Thomas, Margaret and Arthur (see all below).
2 Richard BLAYNEY bpt. 22Oct1718 (Llanmerewig);
bur.Dec 1718 (Llanmerewig)
2 Richard BLAYNEY of London;
Probably a taylor and/or warehouseman, although one tradition had him
as a shoemaker.
bpt.20Jan1719 (Tregynon) 
but living in London by 1758 (mentioned in the will of Thomas)
Previously thought to be the haberdasher of 156 Cheapside [see the Blayney London], but that has been
shown to be Richard son the Rev Richard Blayney.
As Richard died 2Jul1773 (bur. St Alphage, London Wall), he could not be the Richard who
was in partnership with James Smith until 1787.
Father's will of 20Dec1758 mentions Richard had three children.
+ Mary m.≤1754
A Mary SPENCER married a Richard BLAGNEY (?mis-transcription) m.11Mar1746 (London, Middlesex) 
[see Comment 3 about the children's names]
3 Thomas BLAYNEY
b.14Aug1754; bpt.29Aug1754 (Parish of St John, Westminster)
See Thomas, my direct ancestor
3 Mary born/buried 24 Sep 1756 in churchyard of St Mary the Virgin, Aldermanbury;
3 Richard b.24Mar1758 (St Alphage)
Little is known about this Richard. However, his age, name and location fits with
the Richard apprenticed to William Faden ,"cit. & stationer" in London 3Dec1771 [646b]
It is possible that he was the Richard whose warehouse business partnership with
one John Adamson was dissolved in May 1789 and
very likely to have been the unknown male Blayney below.
3 Ruth b.18Nov1759 (St Alphage)
3 John b.17Feb1763; bpt.13Mar1763 (St Alphage)
3 Ann Ruth b.28Sep1764; bpt.21Oct1764; d.21Mar1796; bur.Mar1769 (all St Alphage)
3 Martha b.7Feb1766; bpt.9Mar1766 (St Alphage).
3 a unknown BLAYNEY ?Richard b.24Mar1758 above
as the family were living on the same "Old-Street Road" and with
the same family occupation (Tailor).
4 George BLAYNEY alive and married in 1822, working as a Tailor employing an apprentice
+ ANN ___ alive and married in 1822  ]
5 unknown children but based on dates and location, most likely...
4 ? Jonah BLAYNEY b.25Jul1816 (St Leonard's, Shoreditch)
5 Richard Jonah BLAYNEY b.1845 ; 
+ Elizabeth GILBERT m.9Sep1867 (St. Matthews, Bethnal Green, London)
6 Rose Matilda BLAYNEY b.1888 (Old Ford, East End)
+ Charles Edwin WINGROVE b.1875 (Poplar);
m.17Aug1914 (St. James Church, Forest Gate)
Previously married to Rose's sister, Emma Mary BLAYNEY
7 four children, born 1921-1928 all in West Ham R.D.; Alexander L.,
Gladys I.M., Eileen D.V. and Doreen M.M. WINGROVE
6 Emma Mary BLAYNEY b.1880; d.1914 (Bethnal Green) in childbirth
+ Charles Edwin WINGROVE b.1875 (Polar); m.1897 (Bethnal Green)
Subsequently married Emma's sister, Rose Matilda BLAYNEY
7 seven children, the 1st 2 born in Bethnal Green:
Charles Edwin b.21Jun1898, d.1970; Walter George b.28Dec1899,
Emma Florence b1901; Lillian Lena b.1903; Daisy Violet b.1905;
Rose Mary b.1907 and Frederick WINGROVE b.1912.
2 Marjery BLAYNEY bpt.11Apr1722 (Tregynon) ; m<1758
+ John BLOCKLEY
4 John BLOCKLEY
4 Thomas BLOCKLEY
4 Margaret BLOCKLEY 
2 Elizabeth BLAYNEY bpt.8Dec1723 (Tregynon) 
2 Ann BLAYNEY bpt.2Dec1725 (Tregynon) 
2 Mary BLAYNEY bpt.22Jan1727 (Tregynon) ; alive 1758
+ Richard Davies m.1763 
2 Thomas BLAYNEY bpt.24Aug1729 (Tregynon)  alive 1758
This is likely to be the Thomas BLAYNEY who married Anna JONES
First found farming in Bettws from c.1759
Probable ancestor of the Blayney-Percival "African line",
based on time, place, the use of the family name Arthur and DNA evidence
(which traces this line to the Montgomeryshire Blayneys) .
+ ?Anna JONES
3 Thomas BLAYNEY (1729-1812), of Glyn Farm, Bettws Cedewain
2 Arthur BLAYNEY (BLANEY) b~1735 d.14Jan1788 aged 53  Occ wheelwright  of Llanllwchaiarn .
+ Jane BRICK b~1732 m.19Sep1763 d.22May1803 aged 71  bur.25May1803
3 Arthur BLAYNEY (BLANEY) Junr b.1764/5 d.1833 of Pwll Coed 
Publican; bur.24Jan1833 Llanllwchaiarn
+ Letitia (Letty) OWEN(S) of Newtown m.19Jun1785
Third dau of Mr Owens of Dolfor
4 Arthur BLAYNEY b~1783 Occ. violinist (well known) 
"Blayney the Fiddler" 
+ Sarah TIBBOT b~1790 m.4May1811 at Llanllwchaiarn
dau of John TIBBOT, weaver, & Mary HOWELS of LLanllwchaiarn
5 Mary BLAYNEY bpt.24Apr1814 (Llanllwchaiarn)
5 Harriet BLAYNEY bpt.22Apr1816 (Llanllwchaiarn) ? d.y.
5 Sarah BLAYNEY bpt.4Apr1817 (Llanllwchaiarn) alive 1825
5 John BLAYNEY bpt.6Feb1820 (Llanllwchaiarn)
5 Harriet BLAYNEY bpt.24Jun1821 (Llanllwchaiarn) ? d.y.
5 William BLAYNEY bpt.13Oct1822 (Llanllwchaiarn)
5 Jane BLAYNEY bpt.6Jun1824 (Llanllwchaiarn)
5 Thomas BLAYNEY bpt.28Aug1825 (Llanllwchaiarn)
Possibly the Thomas Blayney who was born
about 1820 in "Newton, North Wales" and died in a Lead
Mine accident 29Nov1875.
Ancestor of some other New Zealand and Australian Blayneys
5 Elizabeth BLAYNEY bpt.27Mar1831 (Llanllwchaiarn)
5 Harriet BLAYNEY bpt.10Aug1834 (Llanllwchaiarn)
? Third time lucky!
4 Thomas BLAYNEY bpt.25Sep1785 (Tyn-y-Coed, Llanllwchaiarn)
Third son of Arthur & Letitia of Tyn-y-Coed
Occ. Harpist, won the prize at the Carmarthen Eisteddfod 9Jul1819.
Noted as a renown harpist by historian Thomas PRICE (1787-1848),
and his "brilliant playing" of the triple harp was responsible for
its popularity in South Wales. 
He kept a public-house at Lydney (Lydbury) Nth, near Walcot and
became the family harpist to Lord POWYS in 1829 but died soon after.  
See Blayneys in Lydbury North
4 Jane BLAYNEY bpt.6Aug1793 (Llanllwchaiarn)
4 Mary BLAYNEY b.1796 d.1Mar1797  bur.4Mar1797 (11mths) (Llanllwchaiarn)
4 Mary BLAYNEY bpt.3May1801 (Llanllwchaiarn)
3 Mary BLAYNEY bpt.10Nov1766 d.4Aug1775  (Llanllwchaiarn)
3 Richard BLAYNEY b.1768 bpt.17Jan1768 (?of Tyn y Coed) of Bettws
Hall ; d.17June1842 (gravestone )
Probably the Richard Blayney of Bettws Hall alive 1839
The 1839 map of "Betws Cedewain"  has the comment
"At Betws Hall lived the 70 year old Richard Blayney."
He is clearly a landowner and the 1851 census reveals
his daughter Margaret head of a household of 28 at
Bettws Hall, with two House Servants and six farm
labourers for a farm of 280 acres.
+ Ursula HAMER b.1766/7 (Llandinam); m.2Nov1790;
d.24Jul1851 aged 84 (tombstone )
4 Arthur BLAYNEY/BLANEY (note spelling change) bpt.27Sept1794
+?Elizabeth d.21Jul1895 aged 63 of Newtown)
5 Elizabeth BLAYNEY/BLANEY bpt.27Jan1822
5 Sarah BLANEY bpt.21Mar1824
5 Jane BLANEY bpt.05Jan1826
5 Ursula BLANEY bpt.05Oct1834
4 Richard BLAYNEY bpt.18Sep1796 (Llanllwchaiarn) [or23Oct1796]
4 Thomas BLAYNEY bpt.18.Nov1798 (Llanllwchaiarn)
4 Jane BLAYNEY of Bettws Hall; b~1800; bpt.11Jan1801 (Llanllwchaiarn)
d.23Dec1864; Unmarried in 1851 (census)
Bettws Hall subsequently passed to Hugh Darby Owen (d.1868)
4 David BLAYNEY bpt.10Nov1804 (Llanllwchaiarn)
4 Margaret BLAYNEY b~1811 (30 in 1841 census, 40 in 1851 census);
?d<1864 unm when Jane died and Bettws Hall passed from family. 
Presumed grandchildren of Richard & Ursula
3 Thomas BLAYNEY bpt.26Jul1772 (Llanllwchaiarn)
+ Margaret OWENS (OWEN) b~1776; m.4May1804 (Llanllwchaiarn)
dau of Richard OWENS (farmer) & Margaret
4 Thomas BLAYNEY b.21Apr1807; bpt.23Apr1807
3 Jane BLAYNEY bpt.11Feb1776 d.3Jun1792  (Llanllwchaiarn)
+(3)Jane HUMPHREYS m.14May1733 (Bettws Cedewain)
Third wife of Thomas of Llanllwchaiarn of Llanllwchaiarn
d.Jan1757 bur.8Jan1757 (Llanllwchaiarn) 
Parish records from this area and time were destroyed in the Blitz of 1940 on, due to fire or water damage but T. Muff has done a wonderful job of piecing together what information can be obtained to generate a much clearer picture 
Why, one might ask, does Thomas, the oldest son of a landowner (Richard BLAYNEY of Ucheldre, Bettws Cedewain and of Llwyn Coch) with close family links to royalty, along with his oldest surviving son and youngest brother, need to take up trades like wheelwrighting, shoemaking and haberdashery? Could it be the mythical "religious feud", the suggestion that they became non-conformists?
Furthermore, we see the youngest son of our Thomas (Arthur of Llanllwchaiarn) have some interesting sons. The oldest, Arthur BLAYNEY (Junr) of Pwll Coed became a publican and had two musical sons, the famous harpist Thomas BLAYNEY and the not quite so famous violinist Arthur BLAYNEY (probable father of the Thomas who died in a mine accident). The second son, Richard (1768-1842), for some reason inherited Betws Hall and farm (280 acres) and by 1851 his daughter Margaret was "head of a household of 28 at Bettws Hall, with two House Servants and six farm labourers". Could it be that this Richard may have returned to the 'established church" and thus inherited? (But from whom?)
After Richard Blayney of Ucheldre died in 1721, his 3rd wife Dorothy Newell married Arthur Howell of Castle Caereinion. Of Richard's sons, only Thomas is mentioned in his will. There is a lack of consensus as to whether this Thomas He was born to Richard's first wife (Ann Hodson), although S P Thomas and Robert Blayney suggest a Thomas was born to Richard's second (Margaret Worthington). Thomas married Anne (Ann/Anna) Jones. He was a wheelwright and/or a farmer who moved around Montgomeryshire. S P Thomas and Robert Blayney believe that his son (also Thomas) also farmed and moved, finally settling on the Vachir farm in 1778, dying 1812 and his son (yep, another Thomas) was "of Glyn Farm, Bettws" , [226 p30], suggesting these Thomases didn't inherit Bettws! Of the other sons of Richard, we have: James, who died in his 1st year; our Thomas (most likely identical with the other Thomas), who became a wheelwright; Richard, who married a distant cousin and had no legal heirs; and Edward who became a shoemaker. No obvious answer there.
The explanation, it turns out, is that Richard Blayney of Ucheldre and his father James were not wealthy and Richard was just leasing "Rectory or Parsonage of Bettus & all houses buildings lands tenements glebe lands by therfor to the said severall Rectory belonging", the freehold having been sold off in the 1630s, presumably by Richard's grandfather Thomas or his father James (who was living in Westminster), to the Gregynog estate (of his relative John Blayney, Thomas's father's 2nd cousin ie his 2nd cousin once removed). In fact Richard moved on to another propery, Llwyn Coch, owned by the Weaver family suggesting he was quite impecunious . His sons would therefore need to obtain a trade or profession or become a merchant if they did not wish to be common labourers or farm workers.
Thomas of Llanllwchaiarn's younger grandson Richard (1768-1842) acquired the lease of Bettws Hall and property from the Owen family (? relatives), who owned the property after John Blayney then Thomas Lloyd .
The move to owners of Haberdasheries, then to actually being tailors, shoemakers etc during the late 1700s and early to mid 1800s in London was reflected elsewhere. A branch of Blayneys in Belfast had also become tailors and boot/shoe manufacturers by the late 1800s . However even this move was not a success and the family in London turned to cabinet making [see the Blayney London], a tradition continuing off & on down to my father.
A rather observant observation by Kevin  supports the conclusion that Thomas of Llanllwchaiarn is the same Thomas that married Anna Jones relates to naming traditions. We see that the children of Mary and Richard (baptised 20 Jan 1719 at Tregynog, the son of Thomas of Llanllwchaiarn) named their daughters thus:
The sons were named:
- Mary the eldest daughter was named after Richard's wife Mary,
- Ruth the second eldest daughter after Richard's wife Mary's mother, and
- Ann Ruth the youngest daughter after both the latter and Richard's own mother Anna Jones.
- There is no Jane,
- The relatively rare name Martha for the youngest daughter most likely commemorates the heiress Martha Loftus (wife of James)
- Thomas the eldest son is of course named after Richard's father, Thomas "of Llanllwchaiarn"
- Richard the second son after Richard himself.
- John the third son is named after an uncle John (a half-brother of Thomas "of Llanllwchaiarn" by his father Richard's third wife Dorothy Newell) and this uncle John, in turn, after John Hodson yeoman of Llanllwchaiarn, father of Ann Hodson.