Why won't my Astra open with key fob any more?

My T reg Astra (1.6 Club hatchback) key fob has stopped working, the car starts but the central locking isn't working. The red light on the fob flashes but the locks don't operate, if I want to lock the car I have to get into the boot and reach in to the rear passenger door lock! Is it a central locking fuse in the car, or loose contacts in the key fob? At the moment I can't even open the key fob either, help!