My wife got caught on this when she came to Ke f with son Jonathan in May. I normally do the Car Hire documentation. I'd booked it but she had to pay when she picked up the car and it seems there was an assumption it would be paid in £ rather than €.
What is even worse is the rip off at the moment by companies offering exchange at the UK Airports. According to the BBC, at Gatwick today, walking were being offered less than a,Euro r or a Pound and parity of the Pound and US Dollar.
Will people never learn? Book currency in advance in the UK or else get it when you arrive.at you destination.