No.
Having number plates which which display both the Euro symbol and the 'GB' letters (in accordance with the regulations relating to size, etc) exempts the driver from having to display a separate GB sticker when driving abroad. So it makes sense for all cars to carry such plates, in order to make things easier if the motorist wants to travel abroad.
So many new cars are sold with such plates as standard, irrespective of whether the vehicle will ever actually be used abroad.
Chris