Update:
Cobra alarm model is 3190. Quite a common one. The Fob is called the 7777.
Managed to get a new fob on line, but programming it to the car was a hell of a job. Luckily, Cobra technical support talked me through it and eventually got the fobs programmed.
PS, I can recommend Southern Car Security. They were v helpful and supplied my new fob.
Alarms etc Did discover that whoever had installed the new alarm, had glued a piece of wood to the bonnet to press the bonnet alarm trip switch. The wood must have moved as it is no longer touching the switch when closed, so alarm thinks the bonnet is open.