BEWARE !! PAY AT PUMP CAN FREEEZE YOUR CREDIT CARD
Pay-at-pump pre-authorises the new fuel limit of £120. Any "change" is NOT released for some days!!!
In these days of belt-tightenng, many people are running close to their limits in many areas.
But using Pay-at-Pump for small petrol top-ups of (say) £30 is going to lock up the remaining £90 credit you didn't use until the petrol station finally gets paid for what you did use.
So for small amounts it's best to pay the cashier for what you actually used.