The barrel in the door just keeps spinning when i put the key in, left and right and the door will not lock or unlock. Does anyone know what this might be and how to fix it. Thanks

Oh its on my girlfriends Felicia not my Superb.

Is the whole lock unit spinning when trying to turn the key or only the central part (The barrel) that is turning?

The barrel, i'm hoping its just a pin or something but the last time i played with one of these it was on my mk2 golf.

It's most likely the spring loaded bit at the back of the lock which is held on by a circlip that engages the lever. It has almost certainly snapped in half.

A lug on the back of the lock barrel is broken or one of the plastic ends on the lock mechanism rods has broken or disengaged.

As idealworld says, it's sure to be the spring loaded lug. If you can get a replacement lock you can change the end over, that way you can use your original key.