Note that you can do remapping of engine ecu at people like KMaps or SAWS tuning. In that case you will have engine ecu with erased need for pairing to alarm ecu. Then you can disable alarm ecu by pulling out the fuse of Lucas system and alarm system will be disabled - but also central locking will be disabled as well, so no use of fob will be present. You will not have passive immobilisation any more as well.
How your insurance will react in this case is up to you and your insurance.