Ford Focus 02 1.6 Zetec Central Locking?

Hi, I'm having a problem with the central locking in that the key does not seem to lock/unlock the doors fully.

When I press the unlock/lock buttons on the key, when I am outside, nothing happens.

When I use the key to unlock the doors manually that works fine. When I am then inside if I press the lock button, it tries to lock but then unlocks straight away.

If I press the lock twice the indicator lights just flash at me.

The boot open button on the key works just fine.

Any ideas why I cannot open/lock the car from outside?