The popularity of erotic fiction such as the bestseller Fifty Shades of Grey could be to blame for the dozens of incidents of people becoming trapped in handcuffs to which firefighters have been called out, a brigade said.

London Fire Brigade said that in the last three years it had turned out to 79 such "emergencies" - and nine instances of men with rings stuck on their penises - and urged people to "always keep the keys handy".

Third officer Dave Brown said: "I don't know whether it's the Fifty Shades effect, but the number of incidents involving items like handcuffs seems to have gone up. I'm sure most people will be fifty shades of red by the time our crews arrive to free them."