A gas engineer has told how he came across a rat bigger than his dog as he worked at a block of flats.
Tony Smith, 46, spotted the dead rodent in a bush near a children's playground while working close to Hackney Downs in London.
He believes it weighs more than 25lb - and is "about 4ft" long including its tail, although this would easily put it on a par with the largest known rat species in the world.
"This is the largest rat I've ever seen in my entire life," he said.
He took a photograph of his friend James Green, an electrician, holding up the supersize rat to the camera.
Mr Smith added: "I've got a cat and a Jack Russell and it was bigger than both of those."
He said bins are often left open near the estate where he has been working so "these little fellas have a pretty good diet".
Some have cast doubts the rat is as big as it appears in the photo, however.
They include Hackney Council, which has posted images showing how the eye can be deceived.
One shows a member of staff holding a soft toy close up to the camera and then just in front of his face.
In the first picture the toy looks huge - but in the second, which shows its actual size, it looks quite small.
Referring to the giant rat, the council tweeted: "It's probably not that big. Our pest control team are checking it out though."
Guinness World Records says the world's biggest rat is believed to be the slender-tailed cloud rat found on Luzon, an island in the Philippines, which has a body length of up to 3ft 3in.
According to the British Pest Control Association (BPCA), there are two species of rat in Britain - the common brown rat or the rarer black rat.
Its website says: "The brown rat is the larger of the rats in Britain, often weighing over half a kilo and measuring about 23cm (9in), without counting the tail."
The BPCA's latest figures show there were 196,012 pest control call-outs involving rats in the UK in 2013-14 - a drop of 30% on the previous year.