Thanks for the help guys, however, I eventually got the required cable from
www.cpc.co.uk
The 300m quantities on sale most places were too much (both length and price) and the only 100m listing on any of the sites given was out of stock (why does nowhere do 200m? odd...).
CPC seems to be quite a decent place, although more like Maplin (UK people know what I mean) than a specifically PC based site.