how do I get my immobilizer and keys reprogrammed?

I need someone to sort this out for me!!!! I've loused up the immobilizer somehow by using the spare set of keys for ages (which in itself was a nightmare to begin with, as the immobilizer didn't recognize them...but the AA man got us going, it involved taking out the fuse a number of times...) and then reverting to the original set. Now the immobilizer refuses to recognize either set of keys, the battery has gone flat, every web search I do requires a level of expertise I lack, and all I want is for some professional auto electrician of some repute, in the beds area (the van is in Dunstable/Luton) to come and sort it out... please...