Hi John. Why not buy a complete bike? ebikes in the UK are still fairly new / specialist, and you will find it much more cost effective to buy a complete bike rather than attempt to make it yourself.

Also if you buy complete it will mean it complies with he law on what is an ebike and what is not, for basics, see here http://www.kinetics.org.uk/html/uk_law.shtml if you build yourself, you will be looking at (possibly), MOT's and insurance which will destroy any cost saving you are making by not driving