HM Customs & DVLA
http://www.hmrc.gov.uk/home.htm
http://www.dvla.gov.uk/
Use the contact link, dont expect an instant response!

The last time I imported a car from the EU I simply drove into the UK and
declared the vehicle at customs.
Where they charged me some money. However as your car is many years old I
cannot say how they would arrive at a figure. On arrival I then had to drive
it directly to my home address, and had some 7 days in which to register the
vehicle with DVLA and MOT it.I believe a licence plate issued would be for
the year the car was built / first registered

Things might have changed since I did it, and as the car was origonally
registered in the uk and was exported with uk tax paid then quite possibly
there would be no duty to pay.
PS I doubt you exported it, in the true meaning, likely you just drove out
and did'nt return.