Basically the seller claims back for any whole months left after the end of the month they sold the car in. The buy then has to pay for the whole month that they bought the car in.and to buying a car with tax on it already, apparently any new/2nd hand purchase, the buyer has to put tax on it, they can't use the tax paid for by the previous owner.
Going to be a boon for the dodgers.
What it also demonstrates is that the law enforcement people now reckon that they photograph your number plate often enough that they will catch most of the people who try to evade paying.
There will always be dodgers, why we don't just put it on the fuel, so if you only do 5,000 miles you pay for that and if one does 50,000 miles you use the road more, it seems a fairer way and you have to put fuel in and as such you can no longer dodge paying, simples!