Our local pay at the pump station (it's unmanned, so all pumps) has 4 limits that you press for. £20, £50, £80 & £100. When you reach that limit it stops pumping. It does say checking card when you first put it into the slot but if it's checking for sufficient funds, or it's a valid card, before delivery I don't know. I've never seen an 'additional' amount on the balance.
If we fill up elsewhere, the odd one does take a pre-payment amount, but it's all sorted within hours.
The only time we got caught out was in France. On our first fill up, on arrival, it took 100 euros from the card. Then it showed the correct cost for the petrol we had, 18/20 euros, but we didn't get the 100 euros back for 5 days!!! That was on a pre-paid Post Office card. After that we paid for petrol by credit card. It did the same with that card but it was all sorted by the time it came to pay the balance.
