300TDI Alarm

My 95 Disco has developed a really irritating fault. When I unlock it (key only, single button key fobs haven't worked since I got it) half the time the alarm goes off. Re-lock and unlock, sorts it but I know that sooner or later it won't re-set. Was fine up till a couple of weeks ago.
Any ideas?

And on another matter, anyone know a good independant specialist in the South West London area?

Central Locking is operating before the alarm is switched off. On the back of the lock barrel theres a small plastic cam that switches the alarm on/off that could be worn and on it's own it's not a replacable part.

Have a look there may be some adjustment.

Is this the single button Conlog LRSS alarm?....several things could be if it is...