The two most likely candidates as the father of William Garrad both christened sons of that name at St Marylebone Parish Church, on the Marylebone Road, London, during 1811:
I suspect it is couple #2, as the #1 would appear as an 1810 birth in the census forms.
If so, Thomas may have died before 1835 - at which point his wife Mary may be the The will of Mary Gerrad of (Failwells?) in the county of Oxford, drawn up on March 11, 1835 and proved on 27 Sept, 1835, states "all my houses, many goods and chattels" were to be divided between her daughter Sarah & son William Gerrad.