I was staying at a hotel that had six or eight charging points in the car park and it was generally very convenient to do a quick charge to 80% and reasonably priced.
Hertz wanted it back with 80% charge or they'd bill us, and finding an appropriate charger near Heathrow was ridiculous. We tried six different locations: the first one was in a hotel, it had only one charger which was occupied with no sign of the driver. Two were in the car parks of office buildings to which we had no access. One was at a Tesla delivery center and didn't have public access. One was at a gas station where all five of the charge points were unserviceable. The last one was at a single-purpose electric car charging station where there was a considerable queue.
In the end, we had to drop it off with low charge and bite the bullet otherwise we were going to miss our flight.