It all happens behind the scenes. Your registration will be automatically read by ANPR cameras. At a minimum, it'll be logged, but probably also recorded against CCTV footage of you at the pump, and checked against a police DB. If there's a slight delay before the pump kicks in, this is why. Welcome to Britain.

Always check you have a card or cash on you, failure to have the means to pay is treated as intention to steal, as far as the police are concerned. The days where you filled in a form and left ID are long gone.

The only exception may be the handful (and it is a small number) of garages that are unmanned, and may require chip+pin.