It is intended to be an ultra-modern central London office that will serve Google for decades, but the new £1bn headquarters is beset by one of humanity’s oldest-known pests: foxes.

The canines have taken over the rooftop garden of the new “landscraper” in King’s Cross and had an impact on construction – although the company stressed it was “minimal”.

The infestation, first reported by the newsletter London Centric, was confirmed by sources familiar with the construction. One told the Guardian it had been a rolling three-year saga and said some foxes had begun to dig burrows in the perfectly manicured grounds.

“There’s a little hole in the garden where one lives,” they said. “We’ve seen her all around the building – one second she’s on the fifth floor, the next she’s on the garden floor. No one has been able to catch her.”

Others said they have seen fox poo on the grounds of the Thomas Heatherwick-designed building.

Mosh Latifi, a co-director of the London-based pest control firm EcoCare, said they could be living off rats.

“Foxes thrive quite well on rodents – we don’t live more than three metres away from the nearest rat,” he said, adding that he had also witnessed foxes in building sites scouring for food left behind by workers.

Leaky pipes, or even generous handouts from local businesses, could be sustaining the skulk, according to another London pest control expert, who did not wish to be named. “London is a big playground for foxes – they will go absolutely anywhere,” they said.

A Google spokesperson said: “Fox sightings at construction sites are pretty common, and our King’s Cross development is no exception. While foxes have been occasionally spotted at the site, their appearances have been brief and have had minimal impact on the ongoing construction.”

According to a search using the firm’s own search engine, the best way to get rid of foxes is to remove food sources, install secure fencing and fill in any gaps.

It is not the first time a pricey London building has had such a problem. In 2011, a fox called Romeo was discovered living in the Shard. He survived by living off scraps left by construction workers.

Romeo was captured and, after a checkup, released back on to the streets of London.

Facebook had to contend with a family of foxes at its Menlo Park headquarters in San Francisco. They were eventually honoured on the social media site – being granted a set of stickers on its Messenger app.

Plans for the new Google building were announced in 2013, as its first completely owned and designed company site outside the US. The 11-storey building will accommodate up to 7,000 employees.

The 300-metre rooftop garden runs along the length of the building and encompasses the seventh to eleventh floors. It’s believed that 40,000 tonnes of soil has been brought to support 250 trees, with a running track winding through them. The garden was designed to accommodate bees, bats, birds and butterflies. It features a space for dining, deckchairs and a fitness area. It also has an indoor pool.

The nearly 1m sq ft building has been under construction since 2018, and is estimated to be completed later this year.

In 2022, a topping-off ceremony that featured non-alcoholic Pimm’s and luxury canapés was attended by Sadiq Khan, the mayor of London, and Keir Starmer, whose Holborn and St Pancras constituency includes the office.

“This project represents a real vote of confidence in London, in our communities and in our flourishing tech sector,” Khan said at the time.