The form you need is called SVA1, go here: http://www.vosa.gov.uk/ and type SVA1 into the search tool. It should come up with the link!
There is more information available here: http://www.totalkitcar.com/tech_registration.php
After SVA and a pass you need to register the car and get a plate. There’s various ways documented above on the total kit car site. In our case we’re going for the donor age related plate. I don’t think you can keep donor plate, but you can get another plate with the same letter on it.
The form required is a V627/1 which again can be download from: http://www.dvla.gov.uk/
Once you have all forms (and an MOT seems to be required) you can submit them to your local DVLA office. There’s list of offices here once you give them all the paper work it can take between 1 and 8 weeks for someone to come and check the car and make sure all the parts match up with what you put on the form.