a car in disguise

This little tactic from France merits attention: avoiding being towed away by disguising the vehicle as something else.

Given the DVLA drive round looking for tax disks, and the inevitable CPZ rollout will involve ticketing non residents, there's a lot of appeal in covering your vehicle over with a big sheet in the city. Owners of open-top triumphs tend to have to do this anyway, to keep out the water, so perhaps you could get away with it in the controlled parking areas.