What to do about price gouging
Unlike the USA, UK authorities have no civil legal powers in this country to tackle price gouging, unless the seller has a 'dominant position' in the marketplace. That rule should prevent the big supermarkets (or markets such as Amazon or eBay) from playing (or enabling others to play) this nasty trick but seems unlikely to be capable of covering small shops which are exploiting a temporary advantage over other retailers. The Competition and Markets Authority advises only that, "It might be abusing a dominant position if it’s unfair to its customers or other businesses."
There have, however, been reports that the CMA is planning to prosecute sellers - perhaps for an offence under the Theft Act, such as obtaining a pecuniary advantage by deception.
So one should report price gouging in the UK to the CMA, via the link from https://www.gov.uk/guidance/tell-the-cma-about-a-competition-or-market-problem . (I've seen a neat little report notice posted online but was unable to verify the telephone number and e-address on it, so it's safer to use the official form.)