Bought a car a week ago and won't start

Hi,

I bought a used car a week ago from a dealership and it won't start. Been back and forth with dealer over it and he has agreed to give me a full refund. Problem is he won't refund me without the cars logbook which according to the DVLA will only be with me in a few weeks! Is this reasonable? I have phoned CAB and they don't have an answer.

Any help will be much appreciated