There's lots of YouTube videos showing people paying at petrol stations with £20 and £50, and £100 coins. After much arguing, and often police involvement, the petrol stations back down and accept payment as they argue they're not legal tender, they are. They buy the coins from eBay for less than face value.
One guy, Julian Chamberlain, was arrested on suspicion of fraud, no charges followed and he sued the police and was awarded £5000 compensation.