Hi again,
Do you have a copy of the 1851 marriage certificate? If so, what was the name of Joshua's father? I've just re-read through the thread and can't see it, but apologies if I've missed it.
I rechecked the Sonning PRs for any spelling variations that I may have missed first time round. Still no Joshua. Newburychap is correct - there are Jeromes in Sonning but mostly in the 1700s. These may well turn out to be yours, but first we need to find Joshua!!

As I said before, the PRs I have only go up to 1836. There are a couple of baptisms in 1817 & 1819 of children of Mark & Sarah Jerome, but they're still too early.
The only entries I could find which might just be connected directly to your Joshua are:
married 18 Dec 1826 William Jerome otp & Rebecca X Excell otp banns
witnesses: Thos X Chandler & Sarah X Chandler.
buried 19 Jul 1830 William Jerome of Woodley age 33.
I can't find baptisms for any of their children in Sonning. I'm not too good with the local geography but, according to the map, Woodley seems to be between Sonning and Reading. Perhaps any children (possibly including Joshua!) were baptised in Reading? As there's nothing showing up on the IGI, I'm thinking the Reading parish that's not covered by the IGI - St Lawrence, I think.
Alternatively, given that she would have been very young when widowed, did Rebecca remarry and would this give any clues?
Hope that's of some use.

Jill