In reply to Postmanpat:
If they've got some in stock they sell a 50m one for (I think) £80.
They say that's long enough for the big wall there, though dunno if you can get away with shorter.
Off to Awesome Walls in stockport later and think gonna man it up and go for "the awesome wall" there for first time. Anyone going expect to hear much swearing and enthusiastic applications of Scream-Power