300tdi Alarm Immob Issue/Nightmare

Got a 300tdi with what i think is a factory fitted alarm/immob it has the rover fob anyway, few months back i turned ignition off, got out of truck with keys and was chattin away, got back in truck immob had kicked in like usual after a period, i tried to fob it and nothing happened thought it could be battery, luckily i was at tesco, got out locked it with key got battery, changed it went back to truck fob still wouldnt work, unlocked it with key opened door alarm went off still wouldnt start (immob still on) sat there looking like a t**t :doh: with alarm going off and messing about for bout 20mins then all of a sudden it worked. It did this about every 2 weeks until the fob stopped working altogether, luckily i have a spare that one worked fine ........ for a bit....... now its doing the same with this fob, but its gettin even more bizzare now sometimes it will sit there with hazzards flashing and sometimes lets me start it and they wont go off, but more recently i've been getting into it trying to fob it and its failing as usual but sometimes the dash wont even light, then it starts chirping away randomly (not the usual alarm sound) i disconnect the main battery for a few mins, reconnect it and its worked the past few times but if this fob fails im goosed..... as u can tell this is a proper pain in the ass, anyone any ideas, or anyone know how to rip it out or by pass it or even fix it???