The vermin have reportedly been sighted after entering buildings via toilets. Fears of giant rodents have continued to grow after reports emerging from Liverpool last year.
And now Andrew Dellbridge, boss of Ace Pest Control, has said the rats are getting “bigger and braver”.
Mr Dellbridge told Norwich Evening News: “They used to work around us but now they’re gaining access they wouldn’t have attempted before.
“They’re letting themselves into people’s houses and businesses.”
Mr Dellbridge has sent the stark warning to residents to keep an eye out in their toilets for the arrival of the rats.
He said: “I was called out to one job in Norwich and the customer could barely speak, she was in so much shock.
“She’d been using the bathroom and heard a noise.
“She looked down and it was in the toilet bowl.
“And this is happening more and more frequently.”
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Mum-of-two Becci, who has lived in Hattersley for three years, had contacted pest control three times to complain about the number of rats in the area.
She said: “The whole estate is just absolutely overrun by rats now.
“When I first moved here there was one living under my floorboards, but now there are more of them.
“I spoke to my neighbour and she said it’s the same in her house.
“Recently, it seems to have become a problem for everyone living here.”
According to the Metro, London had an increased number of sightings last year, with a reported increase by pest controllers of 78 percent.