I find that large diameter heat shrink sleeving which is large enough to
passes over wide parts of my cables does not contract enough to hold the
actaul cable when they are heated heated.

Is it possible in the UK to buy just one or two rolls of heat shrink
TAPE? I mean something similar to regular self-adhesive PVC insulation
tape but which contracts when heated. Does such a thing exist?

My web searches such as this one at Farnell's http://snipurl.com/skla
return heat shrink SLEEVES which is not what I want.