This place on Hatfield Rd might be of use. If they are still there. I've been meaning to use them myself for over a year, I still have one sigma remote left so not in a massive hurry. But after hearing your story maybe I should do the precautionary thing!
Anyway, they are called: In Car Electrics, 227 Hatfield Rd - tel:01727844464
Hope it helps.
Gareth
April 2008