This afternoon my alarm stopped working the central locking. The alarm will set and unset, it will also lock the doors, but it won't unlock them

The alarm is the standard fit one on a MY 02 UK car.

 

sounds stupid but do you have a spair 'plip' ? i would also suggest leaving the battery unplugged for a good few hours then restarting ( take it its fully charged ? ) funny enough my landrover did this at the weekend and doing exactually this seemed to 'reboot' the system adn make the alarm work again,