I put in £3 worth of fuel the other day but that's because it was a rental car that I had to return with the same fuel level as at pickup and I'd only done ~30 miles with lots of stop/start. (I would have used a Zipcar/Zipvan but they've all gone now.) I would have tried to put in less but UK fuel pumps usually mandate a minimum of 2 litres which is not far off £3 at current prices.
Out of curiosity how does that work (never been in a situation where I have to worry about minimal fuel purchases) - does the pump simply round up the price to the minimum when done, or did you actually have to dispense extra fuel, either into a jerrycan or donating it to someone else's car otherwise the pump would not actually finalize the transaction?
It's mandated by a sticker saying so. I don't think it's ever enforced.
A google seems to show that it is because the pumps are not certified to be accurate below 2 litres (or 5 litres for higher flow rate pumps like the HGV diesel pumps) so anything below this is at your own risk.
Another way of thinking about it is you have no right to complain if you think you've been short fueled if you don't dispense the minimum stated.
