If you only want the central locking to work, ie no alarm then why not fit one of these?
Easier than a whole alarm system
I could send you a pin out list that will show the wiring for a meta m99t2 if that's was your original alarm - would help you fit the kit above. Probably only 4 or 5 wires needed
I'm guessing it was a meta alarm however I haven't had the chance to check it due to the rain
the alarm siren is still in situ as I have checked it under the front wheel arch
If you have the details then would be much appreciated