My advice is dont bother.
I have ridden a 35mph capable Golden Eagle (I used to have the same kit as the one mentioned on NACC but it got nicked) for over 2 years around my town and nary a single problem apart from the odd idiot driver. I got pulled over once on a combination of 'I wanna look at her legs' and 'silly girl isnt wearing a helmet and doing 30mph round a roundabout'. They just let me get on with it after they'd had good look at me and the bike.
To go legal you'd have to get SVA - go through a shed load of useless information all for the priveledge of paying shed loads of insurance and most likely road tax for something that is merely a bike with a chainsaw or similar strapped to it. Its not worth the money, hassle and time.. not to mention the fact that the more people start registering these machines the more the govt is likely to kneejerk and ban them..
Jemma xx