“God, I’m glad I never went to that one,” says Neil Hargreaves, as the closing credits of The Lighthouse roll. Neil is a former lighthouse keeper. I have brought him to see the film – centred around a 19th-century brick phallus on a godforsaken, storm-lashed rock off the coast of Maine – to get the insider’s view.

Actually, first I tried to take the film to him, to the cottage owned by Trinity House where he lives in Harwich, with a view from upstairs over the North Sea (tame today). But the DVD didn’t work, so he gave up his day and came back to London with me, to go to the cinema.

To be honest, I was a little apprehensive: what would Hargreaves – 73, old-school gent, proper polite – make of Robert Eggers’s nightmarish monochrome psychodrama? Of Willem Dafoe and Robert Pattinson going fabulously and terrifyingly insane in oilskins and knitwear? Of the flying semen, the unspeakable depths to which they plunge, all the way down to Davy Jones’s Locker? But he remains sanguine and stoic. “From a cinematic point of view, it was quite interesting,” he offers. “There is nothing entirely realistic about it.”

So, er, it doesn’t reflect his own experiences? “Oh no, no, no,” he says, quickly.

Hargreaves, originally from Lancashire, spent 16 years on lighthouses and lightships before taking voluntary redundancy in 1988 and becoming a security guard. He could see the end coming, with automation; since 1998, the UK has had no manned lighthouses.

His wildest, most remote posting was the Smalls Lighthouse, a granite tower perched on a rock 20 miles off the coast of Pembrokeshire, where he worked for two years – one month on, one month off, like in the film.

A key difference, though, was that there were three of them. That came about after an incident on the Smalls, a little before Hargreaves’s time in 1801, that changed lighthouse policy. It was before radio, he explains: the two keepers had no contact with the mainland and one of them died. “The other chap didn’t want the authorities to think he had bumped him off, so he kept him on the lighthouse, first inside the kitchen. Then, because they were overdue due to bad weather, he must have started to smell. So he took him out and lashed the body to the gallery round the outer part of the lantern. By the time the ship eventually got to him to relieve him, he had gone mad.”

Neil Hargreaves in 1987 while serving on the Longships lighthouse, off Lands End

Hmm, a few echoes of the film there. After that, there were always three men on a lighthouse. “They were a good bunch of blokes,” says Hargreaves. “I made some good friends and I’m still friends with them. You got the odd one now and again, as you do anywhere, I suppose. The job did attract the odd loner, people who prefer their own company.”

Most keepers had hobbies; he knew a couple who knitted, like Pattinson’s character. Hargreaves made ships in bottles; yes, he spotted the one in the film, floating past in the drunken madness. The pisspot rang true, too; in the Smalls, it lived outside the shared bedroom halfway up the tower, by the window. “There was a streak down the side of the lighthouse,” he says. For poos, it was “bucket and chuck it” from the gallery.

Was there as much masturbation as in the film? “I suppose you’re only blokes, stuck out there a month at a time; some of that might have gone on.”

Did he ever feel like bumping anyone off? “It only happened to me once,” he says. At the Smalls, his first PK (principal keeper; a lighthouse had one principal and two assistants keepers) was an alcoholic. Lighthouses were dry, but this guy would be drunk going out “and you’d have to send him to his bed out of the way for the first two days”.

He was not the problem, though. When he was eventually sacked, it was his replacement who was the problem. “He was a bigot, a racist bigot. Homophobic as well. Watching TV, he would be cursing and moaning and going on about the … He was a real Alf Garnett, in spite of the fact that he knew my wife at the time was from the West Indies.”

Jesus, imagine being stuck on a lonely tower on the edge of the world with Alf Garnett! Instead of killing him, Hargreaves wrote to Trinity House and got himself transferred, to a platform on the North Sea where he spent seven years.

The gulls strike a nostalgic chord for Neil. There is one in the film who taps on the window with its beak, not in a friendly way, and it ends badly. Hargreaves never did that, but he remembers one they used to feed. It had only one leg and had to perform “a sort of crash landing”. He never saw, or did anything with, a mermaid. He did see a lot of lovely sunsets, though.

When Hargreaves left the job in 88, there were 174 keepers working. Many of them are no longer around. There will be a time, in the not too distant future, when there will be no one left who worked on a lighthouse. That is partly why he founded the Association of Lighthouse Keepers. “It wasn’t a job I wanted to walk away from and forget about.”