Well...if you're anywhere near Lincoln, the good folks at the Lincolnshire Archives may be able to help you. Since I live in Orstraylia (Happy Oz Day - Jan 26th - been drinking beer and watching cricket!) it's nearly ten years since I managed to go there, but they struck me as pretty helpful. Can't remember the address, but it shouldn't be too hard to find on the net.
If you live any sort of distance from Lincoln, find the closest Latter Day Saints (Mormon) church which has a family history centre and find out if they have a microfilm available for that parish. It costs $6 in Oz to hire them, so maybe 3 pounds or so in UK, and you might have to wait a few weeks for them to get it in. You then get a month in which to go in and scan through the film on a microfilm reader.
I may be telling you stuff you already know, in which case ignore me

. The folks at the LDS church are friendly and very helpful by and large, and in my experience make no attempt whatsoever to convert you to their brand.
Have you tried their website
http://www.familysearch.org ? I quickly found your John Cordock baptised 14 Jun 1807 at Keelby.
Good luck!