A woman was left horrified after she spotted a giant rat outside her home in north London.

Sam Firth photographed the rodent, which she estimated to be between 16 and 18 inches, as it peered through her back door in fashionable Belsize Park.

The sighting comes as pest controllers revealed the shocking epidemic of mutant rats - some as big as cats - across the UK.

The rodents, which have been seen been seen across the country over the past year, are twice as large as normal species and cannot be killed with traditional substances.

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Alarming: Sam Firth spotted this giant rat outside her home in fashionable Belsize Park, north London

Fearless: The rodent, which Ms Firth estimated to be between 16 and 18 inches, approaches the back door

One rodent measuring 20-inches was recently spotted at a food establishment in Swindon, Wiltshire.

Kevin Higgins, of the British Pest Control Association, said rat numbers were going up by about 15 per cent each year - and the boom was driven by the availability of food.

'The more food, the more rodents it will attract,' he said.

John McNeice, director of Scottish Pest Control Services, said: 'We see big rats in cold stores. The rats grow a very thick fur. That can make them look bigger.

'You might see a rat under a pallet that looks as big as a cat.'

Similar stories of giant rats have been reported by pest controllers in Glasgow, the Scottish borders and Swindon.

Last week, experts warned of a plague of super rats after it was revealed that pest control budgets have been slashed by a quarter by local authorities.

Information released to Labour by councils has revealed deep cuts in the amounts being spent on controlling vermin.

A map details where notable rats have been recorded across the UK since 2010. The rat discovered in Swindon this month was giant at 20-inches, but not considered 'mutant' as it was killed traditionally

Across 200 local authorities in England, pest control budgets have been cut by 24.4 per cent on average since 2010. There has also been a 16 per cent cut in the amounts spent on street cleaning.

Some authorities insist they have taken steps to provide better value for money, accounting for reductions in budgets.

But others admit they have stopped providing pest control services altogether.

THE RISE OF THE SUPER RAT Super rats are typically larger than sewer rats and cannot be killed by traditional rodenticides. The species has developed a genetic mutation which means substances approved by the EU to control rat populations has no effect on them. Pest controllers are calling for new rules to be made allowing the creation of stronger poisons, though the health and safety risk to humans and the environment this bears is a bone of contention. Most rats are found in food premises, though some have been recorded across the UK in homes. To prevent the creatures from infesting your home or business, experts advise keeping conditions spotlessly clean. Ensuring wheelie bins have proper drain holes is also important, said exterminators. 'A rat in the wrong place is a problem for anybody so you have to be vigilant whether its commercial or residential. 'They'll chew water pipes, electric cables and it puts your property at risk,' said Justin Holloway of exterminators, Prokill. Advertisement

Traditionally, people have been able to call out pest control officers from their local authorities if their homes are infested with mice, rats, wasps or other pests.

Many councils have offered free assessments, and then made subsidised charges for proofing, poisons or other recommended measures.

The decline in local authority services means more people are likely to attempt ineffective and sometimes dangerous DIY solutions, increasing the numbers of pests, experts said.

Reports this year suggest that rats in the UK are becoming bigger, and some are developing resistance to traditional methods of control.

So-called 'super rats' are expected to outnumber humans two to one by next year.

Genetic testing by Huddersfield University has revealed that some rodents have developed a mutation that allows them to survive conventional poisons.

In counties including Berkshire, Suffolk, Surrey, Wiltshire, Hampshire and Kent, all the rats tested were found to have immunity to poison.

Earlier this year, worried homeowners shared photographs of the rodents, some of which were as large as small cats.

One, found on an industrial estate in Liverpool, measured two feet, while another in Gravesend, Kent, was the width of a shovel.

Researchers at Huddersfield University performed studies on the rodents, with some parts of Britain more severely affected than others.

In Gloucestershire and Shropshire, around 20 per cent of rats tested were immune to traditional poisons, while a third in Kingston could not be killed using the substances.

In Southampton, 75 per cent of the rodents were found to have the genetic mutation.

Spread: This enormous rat discovered in Cornwall last year measured 50cm. Reports this year suggest that rats in the UK are becoming bigger, and some are developing resistance to traditional methods of control