Thomas Leath Clayton was the son of Robert Clayton and Mary Ann Leath .
Name: Robert Clayton
Spouse's Name: Mary Ann Leath
Event Date: 06 Jun 1759
Event Place: Caistor-Next-Yarmouth, England
He was born in 1773 and was married to Catherine Heath sister of William Heath.
Name: Thomas Leath Clayton
Spouse's Name: Catherine Heath
Event Date: 19 Mar 1789
Event Place: Norwich, Norfolk, England
Their children :
1.Catherine Clayton 1789
2. Harriet Heath Clayton 1791
4 Susan Heath Clayton 08 Sep 1793 died 1798
7.Philip Clayton who married Martha Scott
8.Mary Clayton who married Arthur Brantaugh Beevor
Thomas Leath Clayton and his parents. The birthplace 'Yardsmouth, Lancashire' for Thomas Leath Clayton should be Great Yarmouth, Norfolk. The source of this info is Great Yarmouth, St. Nicholas Church, Parish Records. Thomas Leath Clayton's mother is, as you say, Mary Ann nee Leath. For her I have the same birth date - 20 Mar 1735 - and baptism date 29 Apr 1735. I sourced both these from the Acle St. Edmund's (Norfolk) Parish Records - the scanned image is available via FindMyPast. I believe that Mary Ann was born in Acle rather than in Great Yarmouth, because her parents lived in Acle and all their children were baptised there over a period from 1731 to 1745.
The father of Thomas Leath Clayton was Robert Clayton, rather than Thomas Clayton. Robert was my 5x Gt. Grandfather. His life is well documented and there are many references to 'Robert Clayton of Southtown', including his Will, which I would be pleased to share with you if you are interested. Robert Clayton was baptised on 14 Jan 1727 in Lammas with Little Hautbois, Norfolk, where his father (also Robert Clayton) was the Rector. Robert moved to Great Yarmouth and had a linen draper's shop from about 1754 to 1789, when he retired. This Robert lived on Wrestler's Plain in Southtown, which is across the River Yare from Great Yarmouth, so is actually in Suffolk rather than Norfolk (although some of its administrations come under Norfolk). The info you have for this person's (Robert rather than Thomas) death is correct: the historian Charles White records that Robert Clayton died 23 Sep 1806 and was buried in Gorleston on 01 Oct 1806. Gorleston is the neighbouring village to Southtown and, again, is in Suffolk (rather than Lancashire).
This Robert Clayton's eldest son was called Robert, who was my 4x Gt. Grandfather. He was born in Gt. Yarmouth in 1761 and in 1876 he married Mary Heath, who I believe came from either Blofield or Hemblington in Norfolk. I am still trying to find out more about her parents, hence my confusion over the various William Heaths of Hemblington!