Thanks for the replies people !
I just had a look on eBay, and found a reconn'd rack, so might go after it.

The pulling to one side can (but not always) happen just by letting of the throttle. After I picked the car up, the knocking was almost gone ... then it seemed louder on Saturday but has gradually gone quieter.

I've got some new discs to go on anywho, but I was going to wait until I know for sure what the knocking is.
My mate at the garage is pretty sure its the rack, he shook the wheel (on the side where the knocking is coming from) and could hear it, he also noticed its slightly worn ... and the knocking sound would be louder when driving as its getting more of a beatin'


Thanks again