It's funny, as a Brit I was reading this and wondering whether the prices were so cheap as to be laughable or so expensive to be equally laughable. I soon realised it was the latter!
I'm not sure that proper supply and demand really applies in the UK. There is so little demand that it seldom becomes a driver. Sadly, we largely take what we can get and adapt. Supply issues from the US have long been an issue as the market is so small and shipping relatively complex that it's not a major market and that is reflected in the price and availability of everything. Bullets, brass, reloading equipment......and guns.
The upside is that many UK shooters are (mostly) equipment agnostic and there is little brand loyalty. That's not because they don't have preferences but because there are continuity of supply issues so alternatives are needed. We also find that when the US market overheats (threats of controls=massive sales in all commodities) there is no chance of anything heading across the pond hence we look elsewhere and, on occasions, we strike lucky.
I love the irony of a nation with such incredibly restrictive gun controls producing shotguns/double coveted the world over.....but struggling to get reloading components for them lol.