Hi, Hugh,
The obvious answer is to replace the pipe! You don'y say if its a metal or rubber pipe. If it's metal, try Chemical Metal from Halfords or B&Q. Dry the pipe off first, clean the surface if you can with emery cloth to get a good grip and smear the stuff on. It's cheap and effective. But do make sure the pipe's dry before you put the stuff on 'cos it won't stick otherwise.
If it's a rubber hose, try self-amalgamating tape. It's a strange adhesive tape that bonds to itself and forms a good seal over rubber. If you have a Maplins store near you, they sell it. You may be lucky in B&Q or a builder's merchants perhaps.
Don't fiddle about with stuff like Radseal...it doesn't work on a leaking pipe. Depending on what the pipes made of, these two ideas should sort the problem out. But do make sure with either one that the pipe's dry before you do the job.
Best of luck.
Denis (CarAid Mobile Repair), January 2008