Just copied this from the DVLA website.


If you are the keeper of a vehicle and you do not license it because you do not use it or keep it on a public road, you must tell us as soon as you take the vehicle off the road. Telling us about this is called declaring SORN (Statutory Off Road Notification). This also applies if you have recently purchased a vehicle and the previous keeper has declared SORN. Once you have made a SORN declaration you will be sent an acknowledgement letter within 4 weeks confirming the details. If the acknowledgement letter is not received after 4 weeks you must immediately contact Customer Enquiries Group on 0870 240 0010.

You only need to make a SORN for a vehicle that had a licence in force on or after 31 January 1998.

HTH

Martyn