Bellwire -
http://www.screwfix.com/prods/17428/...ire-White-100m
That would do the job, provided its not a long run, but you'd have the problem of being able to tell which is positive and which negative as its not marked. If you have a multimeter to check then your OK.
Screwfix do a 2 core flex:
http://www.screwfix.com/prods/14444/...Round-Flex-50m which I assume would be colour coded and if so would be OK too.