Rather create a new thread I'd like to share my experience here with Abacus Car Alarms. A very nice guy called Sam explained all the details to me, was very nice to deal with and very quick at getting the job done.
Basically as it says on the website above, I had to take out the meta alarm from my 3200 (a walkthrough of how to do this is on the website) and send it with the circuit board from my working fob, by special delivery. Sam called me the next day, confirmed he'd received it and we discussed what I needed. I paid him £210 for reprogramming the alarm and two new fobs, and I got these and my alarm the next day.
So now I have the original key (the only one I had when I bought the car, no red key), a spare key (not Maserati) that has a chip for the immobiliser, and two spare fobs that work the alarm/central locking. Result! For me it was definitely better than chucking £3k on a new ECU and locks etc.
Still waiting on a new siren from eurospares, that will complete the package for a working alarm...