Most beekeepers in the UK are hobbyists, with there being about 300 commercial beekeepers to ~40,000 hobbyists, with the average hobbyist managing between 1-8 hives.
Because of the economies of scale, commercial beekeepers can produce bulk amounts of honey and sell it for cheap. In fact, much of the honey sold in UK supermarkets is imported from abroad, including from countries where husbandry practices which a British beekeeper would describe as "dubious" or even dangerous for the health of their own bees, and bees at large (diseases spread, y'know). As with what happens when supermarkets enter any kind of market, the supermarkets quickly outcompete local and small-scale producers on price, and marginalise or push them out on the market.
Amateur/hobbyist and semi-professional beekeepers often find it hard to compete with supermarkets and other mass retailers - as I once read a beekeeper say on a beekeeping forum, "Aldi sell 1lb jars of honey for 99p, I can't compete with that, so I don't."
Yes, buying from amateur beekeepers is more expensive. Yes, you can buy cheap honey at the supermarket. But amateurs are the beekeepers in our communities, amateurs are the beekeepers who invest hundreds, or even thousands of their own money in their hobby to help conserve bees and provide a service to their communities. Honey sales help amateur beekeepers to maintain their hobby and even invest in new equipment, which often means, more bees.
Please consider buying from a local beekeeper, a reseller for a local beekeeper (they do exist - in some butchers for example) or an amateur who sells over the internet, before buying from a supermarket.