Sorry it has taken so long to reply but I had changed my e-mail address and had not been checking.
The further I go back is circa 1717 with a Thomas Ascott who Married Joan Seaman in Dec 1737 at Halberton, Devon.
I do have a William Ascott who was christened on the 12th January 1772 at Tiverton, other than his parents (Father Thomas Ascott chr 1st Jan 1740 Halberton and Mother Susannah Trude b31st Jan 1739 -m 26th April 1768 at Tiverton)I have no other information on him.Could he be your William born circa 1780
"Mother is listed as Susannah on the IGI no father mentioned.Christened at Tiverton 12th January 1772.Batch CO51722 Source No. 0917541Printout No. 0933229"