Hi poppymilly
It is suggested on one of the Ancestry family trees, that Thomas Andrew Hendrick 1783 comes from St Lukes, Finsbury. This should be followed up if it hasn't already.
The registers have been deposited at the London Metropolian Archives which is closed to the public until January 2008 while major refurbishment is done. However according to their catalogue the originals are not available, but if some of the registers have been transcribed onto the IGI there should be a film.
From the IGI there is a baptism for Elizabeth Batchelor 7 February 1764 St Michaels, Lewes, Sussex mother Elizabeth, no father.
I think this may be too much of a coincidence with a suggested marriage date of 14 February 1764.
Re: the marriage indexes, although they don't cover all the parishes in all of the county, they are a good place to start. I have the Surrey marriage index and again William & Elizabeth aren't there. Also Boyds and Pallots indexes don't give 100% coverage, but they aren't there either.
So where to go now?
Wait for the LMA to re-open and get St Lukes registers checked out unless this is what you have already paid them to look at. From my own experience a lot of baptisms that are in registers don't make it onto the IGI for whatever reasons. However before 1813 you may not get much more than a childs name and a father.
William & Elizabeths marriage will provve more tricky. You may be lucky and find it at St Lukes, if not it means going through each register for an ever increasing area until it turns up.
In the meantime I suggest you contact everyone on Ancestry who has your Thomas on a tree, explain you are trying to prove a marriage date for William & Elizabeth and ask them for parish names for the dates they have posted. Again you may be lucky, someone might have it on file but not on the internet.
I'll be at the LMA in January so can do the Finsbury look-up for you then.
Dawn