Just to clarify for you simon, the pump is run on the s1 via a mechanical propshaft from the driveshaft. This isn't a good design and does basically wear out.
The fix is as you have been told an electrically powered pump. This is I think one from a rover of some kind. I had it done as I mentioned and it was a perfectly good fix and never caused further issues. The dealer cost for the fix was over 1000.
As I mentioned this is a known s1 issue and if the car is under warranty you should pursue a claim if your warranty covers this.
