Found this link on the DVLA website. I don't know when it was last updated, but there may be some useful contact numbers on here!? (for sourcing parts etc?)

http://www.dvla.gov.uk/forms/pdf/V765X1_100304.pdf

or if you want to do motorsports events
eg sprints hillclimbs you will need to be a member of a msa affiliated club

http://www.msauk.org/Go_motorsport/Local_contacts.asp