America's unofficial party house where presidents like Trump stay in London

In central London, on land the size of seven football pitches, sits a mansion called Winfield House - the official residence of the US ambassador to the UK.

It may be a stately home but through the years it's been known to throw one hell of a party, especially on 4 July, America's Independence Day. This year's celebration saw Nile Rodgers & Chic headline the building's lawn for thousands of people.

Fashion's elite, sports stars and wartime leaders have all been entertained here. Even in 1825 when the original site was built, according to Winfield's official website, its primary use was for entertainment.

President Donald Trump is spending the first night of his state visit at the 35-room mansion. The Trumps also stayed there in 2019, as did the Bidens and Obamas previously.

"It's not just the home of the ambassador, but it's also a centre of diplomatic hospitality," says Stephen Crisp, formerly the property's head gardener, who worked there for 37 years until his retirement last year.

One thing Winfield isn't, is a tourist attraction. Located inside Regent's Park, it's exclusive and takes planning to get inside. Friends of Regent's Park previously arranged tours of the grounds - but so far this year the ambassador has not granted permission.

From the road outside, the house cannot be seen. It's shrouded in woodland and is very private for central London.

"It's really, really difficult to get in there. I regard it as a feather in my cap that I actually managed to get in," says Viv Ward, Friends of Regent's Park's event manager. He calls the house "magnificent" and is audibly in awe of the grounds.

Tours of Winfield only allow you to see the ground floor, which is basically a "very posh" area for receptions, and the gardens. The first floor is home to the personal apartments of the ambassador.

As a home and the venue of most American receptions, schedules are tight. "It wasn't a case of we would like to come on this date and this time. It was just, you will be allowed to come here on this day," Mr Ward says.

The property boasts the second-largest private garden in central London, says Mr Crisp. It's home to a lawn, paved walkways, sculptures - and there's also space for helicopters to land.

Socialite and heir to the Woolworths fortune, Barbara Hutton, sold Winfield to the US government for a mere dollar in 1946 in an offer described by the then-president Harry S Truman as "most generous and patriotic".

Hutton had bought the house 10 years earlier after it was partly destroyed in a fire. The Crown Estate Commission gave her permission to tear it down and rebuild in the iconic red brick Georgian style that remains today.

She named it after her grandfather, Frank Winfield Woolworth, the founder of the Woolworth shopping chain.

With World War Two about to erupt and her second marriage not going particularly well, Hutton returned to America with her son in 1939. It would later be revealed this is when she met her next husband - actor Cary Grant - who is said to have stayed at the mansion with her.

During the war, Winfield was commandeered by the Royal Air Force balloon barrage unit with officers reportedly playing football in the gardens.

Hutton returned to London to see what was left of it at the end of the war - and after the Germans' bombs. She called her lawyer and requested it be handed over to the US government for repairs - and it's been used as the official residence of ambassadors ever since.

History is in the walls of Winfield. The original building was called St Dunstan's, and according to Friends of Regent's Park, was used for blind veterans of World War One. A charity of the same name still exists today.

Speaking about US presidents, Mr Crisp says: "At some point they all come, at least once." He explains he met Trump and his wife Melania during their previous state visit in 2019, which was "a little bit surreal". They dined at the property with Queen Camilla and King Charles III before he ascended to the throne.

An iconic image of Mikhail Gorbachev - the last Soviet leader - and US President George W Bush may be one of the most famous moments from the house. The pair held a joint news conference there at the G7 summit in 1991.

Politicians have long used it for key moments, including international summits, grand state dinners and bringing together wartime leaders.

Security detail for presidential visits is secure information - often never released. But Mr Ward shares a glimpse into the daily routine at the house.

"The security is unbelievable, I mean for example I used to have to send the embassy a list of attendees," he adds, saying photo ID had to be shown to the armed presence on the gates of Winfield.

And if you want to leave early? An armed officer has to escort you off the premises.

Winfield House has hosted many varied events, says Mr Crisp.

There have been performances by Take That, Duran Duran, the Foo Fighters, Ed Sheeran and Bastille, he says, sometimes in the garden and sometimes in the house.

It's also been home to sporting events with the Duke of Sussex attending an Invictus Games reception there. Michelle Obama got stuck in with a sports day event, even doing the tug of the war alongside some famous spectators.

Fashion royalty has also hit the corridors of Winfield. Former Vogue boss Alexandra Shulman co-hosted a London Fashion Week opening party with the ambassador at the time. A Spice Girl was spotted too.

Some of the events would involve "thousands" of guests, Mr Crisp says, with the 4 July parties typically gathering 3,000 or 4,000.

It's a bit of an escape.

"You would never know you're in the centre of the London," Mr Ward says.

But what's the most disappointing part of the house? (Disappointing feels like a stretch.) Mr Ward says its driveway is "rather modest" compared to the rest of Winfield.

"It's big enough for big limousines but you couldn't get a brigade of guards walking up and things. It's not like the Mall."