How can it be covered if its not had the right amount of tax paid to use the roads? Doesn't matter if the insurance know its a 2.0 if it's still taxed as a 1.3.
Don't see the point in doing it really to save about £90 a year in tax as the insurance is the expensive one to sort out.
Before everyone jumps on me for this I do feel sorry for the owner and agree this should never have happened whatever the owner has decided to tax/insure the car as. I always wait with my cars at MOT's because of things like this but hindsight is a wonderful thing.