It's just before daybreak in Richmond on the southern bank of the River Thames, and pest controller Michael Coates is patrolling the rubbish bins for what is normally an elusive enemy -- rats.

"There'll be something in there for sure," he says, kicking an overflowing waste container. "Rats are like little survival machines; wherever you get reliable access to food waste, they'll keep coming back."

Coates' prey has become more conspicuous in London the longer England's lockdown lasts.

What's more, the animals are on the move.

Pest controllers say that, as many restaurants and office buildings in London's bustling city centre remain empty, rats are forced to migrate to more residential areas in search of food.

Families spending more time at home -- and eating all their meals there -- have led to an increase in refuse and that is luring rats into suburban dwellings. Meanwhile, bird feeders -- kept replenished through the winter -- are encouraging rodents to burrow in backyards.

"We had a case of an old lady who used to feed her beloved robins," Coates tells CNN. "By the time she called us there were maybe 10 to 15 rats digging around the flower beds," he adds.

Paul Claydon, another exterminator, based on the edge of Epping Forest in the capital's east, has seen worse. He says he recently killed off a colony trying to dig into a rabbit hutch to eat an unsuspecting family pet.

"It might be that we are seeing and hearing them more often, working from home in the office under the loft... but I fear London may get a big surprise when it reopens," Claydon says. "Especially if businesses and properties that did have a problem haven't kept up with their pest control plans."

Coates and Claydon have both left long careers in other fields to set up small firms in what has become a booming sector.

Coates, a veteran of the Iraq War, founded his outfit five years ago and has since written an eBook named "War and Pest: from Basra to bedbugs."

Claydon spent 25 years in IT at a financial services firm before setting up his business two years ago. "I wanted something that was recession-proof, and it has been relentlessly busy," he says.

Claydon says he normally gets about 10 rodent call outs a week but during lockdown it's been "easily 20 plus."

The British Pest Control Association (BPCA), which represents 700 vermin catchers across the country, said its members reported a 51% hike in rodent activity during the first lockdown, in the spring of 2020, and a 78% increase in November after another lockdown was brought in. They haven't yet calculated figures for this year but told CNN sightings were up, presenting a public health problem which many homeowners are left to deal with on their own.

"We may see rats now where we wouldn't normally because they are so desperate," says Natalie Bungay, of the BPCA. "Rats can chew through very hard substances like soft metals and brick."

When it comes to controlling rats, London doesn't seem to have an overarching plan.

The mayor's office told CNN the London Councils' office was best placed to respond to questions on the subject. But they said they don't collect data on the issue because that's the job of each of the capital's 32 boroughs.

A spokesperson for the borough of Richmond upon Thames, however, told CNN it does not collect data on rats and does not offer pest control services.

In 2017, after a video of rats pouring out of a flower bed in the borough of Harrow went viral, Conservatives in the Greater London Assembly (GLA) commissioned a report which found more than 100 complaints were logged with councils each day.

Called "Rat Land," it warned the city should get a grip on its rodent problem before attracting the bad press that dogged Paris after similar footage surfaced of their "super rats" crawling all over public parks near the Louvre.

Nobody really knows how many rats there are in London, though some private surveys from exterminators claim they could number up to 20 million. It's likely there are more of them than the city's nine million human inhabitants, whose population growth is slowing, according to the Office for National Statistics.

Rats, meanwhile, can multiply fast. Research by pest control firm Rentokil, cited in the GLA report, claimed just one breeding pair of rats can lead to the birth of about 1,250 in a year.

The size of rats is increasing too. Claydon claims it's not uncommon for him to catch a rat measuring up to 40 centimeters (15.7 inches) these days. Many, he says, require stronger traps and more poison to kill.

Bungay says the best pest control starts with prevention. That means sealing off any food waste outside the house in appropriate rubbish containers, keeping food locked away inside the house and checking all air vents are property protected with steel mesh and cracks filled with steel and cement. The avid gardener should also be aware that compost heaps attract rats, she says.

London residents are also becoming more accustomed to seeing their new neighbors and are alarmed by their boldness.

"I actually saw one come right up to me while I was walking," says Jen Johnson, who lives in the eastern borough of Tower Hamlets.

"I saw another one run up a block of flats and I screamed. I've lived in London for four years and I've never seen anything like it," she says. "They're appearing in places that I used to think were scenic. But now it's like, oh there's a giant rat there. Oh great."

Tower Hamlets, which does offer its residents some free help with vermin, told CNN that "anecdotally, our pest control team has received fewer call outs during the pandemic." However, a borough spokesperson did not provide data to back up that claim and said it does not keep figures on the numbers of rats killed.

The City of Westminster, the borough of Harrow, and the boroughs of Waltham Forest and Redbridge which are both close to Epping Forest, did not respond with any comment by the time of publication.