I purchased an x100 1999 XKR in June, I have always loved these cars, never owned one before. It ran perfectly fine until I went away for 2 weeks and the battery had obviously gone flat, once charged I tried to restart the the car and the system check goes ahead but the car will not crank, long story short I have gone through every fuse, SLM module and ultimately found that the immobiliser has disabled the engine, how do I reset the immobiliser? Have tried to get an auto locksmith to come and have a look at it, but not a single soul seems interested, most frustrating, I am based near Bishops stortford, if anyone has any suggestions as to who I can call, or ultimately if I can sort this out myself, I would be grateful. 

Press the lock/arm button on the fob rapidly about 6-10 times. Also if you have a spare key, check whether it will start with that, it's not unknown for a key with an RFID chip inside for the immobiliser to "lose" it's code and cease to operate the immobiliser disarm.

Are you able to read the DTCs at all?