People over about fifty in England will tell you Halloween "wasn't a thing" when they were young. They are right, and the explanation is a date: 5 November.
The competition
Halloween's traditional business was fire, disguise, door-to-door and mischief. Bonfire Night, which arrives five days later, took three of those four and did them at civic scale.
After the failure of the Gunpowder Plot in 1605, Britain acquired a state-sponsored autumn fire festival with parliamentary backing, an effigy to burn, and — as the technology developed — fireworks. Set that against a domestic evening of turnip lanterns and apple games and it is obvious which one a child would choose.
In England, Bonfire Night simply absorbed Halloween. The fires moved to the 5th. The children's begging moved to the 5th, in the form of "penny for the guy". Even Mischief Night attached itself to the 4th, the night before, rather than to Halloween.
Where it did not happen
The pattern is uneven, and the unevenness is the proof.
In Scotland, the Gunpowder Plot was an English preoccupation and Bonfire Night never took hold to the same degree — so guising, turnip lanterns and Halloween divination continued unbroken. In Ireland and the Isle of Man, where Hop-tu-Naa is claimed as the oldest unbroken tradition on the island, likewise. Pockets of England kept their own local versions — Punkie Night in Somerset, Allantide in Cornwall, souling in Shropshire and Cheshire.
So the accurate statement is not "Britain lost Halloween". It is: England let it fade because it had a better-funded rival, and the Celtic nations never did.
The American return
From roughly the 1980s the American form arrived — trick-or-treating in that phrasing, mass-market costumes, pumpkins, and eventually the full commercial apparatus of scare mazes and scream parks.
It landed on ground that had been cleared, which is why it felt foreign. An English child in 1985 encountering trick-or-treating was genuinely meeting something new, because the native version had been dormant for generations. That is the honest root of the "American import" complaint — it describes a real experience, while being wrong about the deeper history.
Which is winning now
Halloween, comfortably. It has commercial weight behind it and, crucially, it is a participation festival: you dress up, you decorate the house, you go somewhere. Bonfire Night is largely a spectator event, and organised displays have been squeezed by cost, insurance and — increasingly — objections on grounds of animal welfare and air quality.
The scale of the modern UK scare-attraction industry tells the story. Places like Tulleys and Alton Towers now run multi-week seasons drawing hundreds of thousands. Nothing comparable has grown up around 5 November.
The turnip lantern, in the end, outlasted the guy.