The real question is "How can I do it right for the least cash?"
And the real answer is - you will have to be lucky.
Before you do anything else you need to find out if the bike is an import. Call Yamaha UK and they have a section that will tell you, for free, if it is imported from the VIN number. If it is imported, but not registered, you then need a V55/5 and it is a big form and the paperwork to show tax has been paid (if applicable). Plus the fee.
A Yodi check will do several things as, normally, a HPI check is included so you will be able to tell if it is showing on the DVLA batabase and if it is whether it is recorded nicked or written off. If it shows then you have the reg. so just put in as the new owner.
A £25 cert from the RD club will say that the frame would have been produced at a certain time. If it is shown to be subsequently nicked or has outstanding Import tax then you are buggered.
You could look for a frame on evilbay with a V5 and transfer the bits.
Depending on which way you go, you are going to have to spend cash.