I tried changing the water pump but failed and got as far as taking the pipes off. This has now started a leak in the joint between the pump and the metal pipe. I can't fine the rubber reducer. Can any one help? Am I being thick and its a standard bit of rad pipe stretched?

You're not thick but your description lacks clarity. Too many unknowns. It's not clear what you did, step by step, from start to where you are at now. Maybe some photos will help.

Edited 7 June, 201511 yr by RicardoM

I removed the pipe work from the water pump so I could remove the water pump. But that as far as I got as I couldn't remove the engine bracket. So I put the metal tube back then reattached the rubber reducer and the rad hose and filled the system back up. Took it for a drive and found the reducer has a hole in it. So I tried plumbers tape as a temp fix but it won't hold water under pressure. So I need a new rubber reducer the fixes the water pump to the metal rad pipe.

Part number 6U0121051H

That's the part. I have a silicone one on order and hope to fit it Thursday and have the car running. I got it from eBay and ordered a 38mm to 28mm reducer I would post the link but in on my mobile

All done the silicone reducer fitted (with some lubrication) and I found a hole in the metal tube, witch was fixed with a £5 replacement from the scrappy so job done.

So to any one with the same problem, look for silicone joiners. The type for ali pipe you see on "tuned cars" for the size try 42mm to 28mm as mine was a really tight fit, it only just got on the water pump spout.