Basically the driver side lock doesn't work when i turn the key. I can unlock and lock the car from the passenger side, so i assume its not a central locking problem.

If i sit inside the car and push the pin up and down the driver lock will function properly and lock the entire car. Because of this and the fact there is zero resistance when i turn they key, i'm assuming that it's more of a mechanical problem than an electrical one, perhaps the linkage between the key latch and whatever that connects to? It doesn't feel like i'm pulling on anything by rotating the key.

If that is the problem what part do i need to fix it? Or do you think i'm way off anyway?

Cheers in advance guys, don't mean to be obtuse.