When your vehicle is scrapped, you should receive a refund for unused months of vehicle tax from the DVLA. With the new disc-less system, the DVLA will refund every full month remaining on your vehicle tax once you have sent them change of ownership confirmation via section 9 of the V5c
The DVLA state that you will receive the refund within 4-6 weeks, and you should be notified by post once this is complete. There is a full guide to this process on the DVLA website. The section 9 procedure will be fully explained by us when you call to make a donation.