The AA recommendation is to get good legal advice if you get into motoring law issues.
http://www.theaa.com/motoring_advice/legal-advice/motoring-offences.html
Source - the AA - ©2015 AA
Following a recent change to the rules, now when a vehicle is sold, the road tax is immediately terminated. The new owner must buy road tax for the vehicle immediately, or risk being clamped and/or fined. This is the case also for couples who transfer ownership of a vehicle between them, but several people have already been caught out by this change.
The fine/release fee of £200 (halved if you pay within 24 hours) does not include a fee for storage nor a surety (deposit) of £160 for a car or motorcycle, should the vehicle have been removed to a car pound.