Does anybody know the rules about registering a car in Portugal that is bought from overseas i.e. UK - Is it true that you have to pay import duty in order to get a Portuguese number plate ?

yes it is a nightmare...why or why dont you just come here with the money and buy a car from a garage...their are lots of new cars now available at good prices

There is a one-time-only way to get around that, if you move your residence to Portugal the car can be imported as part of your removal - tax free.

For further information on legislation and imports, I suggest you contact local dealerships like 100 I.A. in Odiaxere, they will handle the whole process for you - for a small fee of course - but still a whole lot less than if you got nabbed with UK plates after six months.