Hi Julie,
I'm afraid I can't find the marriage. The only one I can find that's anywhere near is
WILLIAM FULLER to SARAH WAKELING in 1843 at Derby St. Alkmund ( I thought his surname may have been mis-transcribed)
that was from Family History Online, but if your William was born in London and Sarah in Berks, I've no idea what they were doing getting married in Derby! So, most likely the wrong marriage.

Using the Hugh Wallis pages, I searched for a 'Sarah' baptised in Chaddleworth around 1819 on the IGI, and the only one that came up was
SARAH MARIE BLANDY bp 10 May 1818.
Sorry I couldn't help more. Perhaps someone else with have some fresh ideas.
Jill