Snowbe XS Prestige are excellent, as Ron says, and cost approx ?37.
If you don't want to spend that much, Worcestershire lines are probably the next best thing. Made by Shakespeare and from the same factory as the Snowbee ones, but a darned sight cheaper. You can pick them up from ebay fairly regularly from a seller called PitsfordPirate.
Also, what are you going to be using the line for?