Immobiliser issue
 

When starting up my 1995 6.0 coupe today - engine turned over rather slowly due to the effects of the car sitting around and a rather flat battery. Usually, charging it up for a good few hours restores things to normal and the battery is usually kept trickled charged when car is not in regular use. However, after fully charging the battery, went to start the car - all the usual dashboard lights came on, but when key is turned to start position 3, there is absolutely no sign of the starter motor engaging. No clicks from the starter solenoid- nothing. This happened to me once before when stopped to refuel the car and switching off the engine. When went to restart, just got no output from the starter. After locking and unlocking the central locking using the remote a couple of times, the car then started. This time though, although the car is locking and unlocking with the remote plipper and the alarm seems to be working, the immobiliser appears to still be on.
Vehicle Electrics aren't my strong point so I'm looking for some advice or whether anyone else may have had a similar issue.
is there a way to bypass the immobiliser? i don't need it as a security feature on the car. There isn't a valet switch fitted in the centre console by the way, I've already checked that!