I think the main criteria would be:
a/ fully working headlights
b/ plenty of room on the back seats
c/ a lack of sexual inhibitions
( Boris Johnson's Press Secretary, Sat 13 Jun 2009, 2:08, archived)

I see it like an Ice skating comp
with three sections comprising of compulsory, original and free.

and Torvill and Dean
( executiverocker only wears C&A, Sat 13 Jun 2009, 2:11, archived)