McDonald's and Diet Coke - Donald Trump's unique birthday plans as he turns 80 today

The last incumbent in the Oval Office of that vintage was Trump’s predecessor Joe Biden, who Trump famously dubbed “Sleepy Joe” because of his age. Biden stepped down from the presidential race at age 81 because of concerns over his cognitive ability.

Trump has joked, to the fury of his detractors, that the huge garish structure outside America’s most famous residence could become permanent, declaring recently that it is "attractive to a lot of people", adding it could be like when Paris decided to keep the Eiffel Tower.

“He’s a showman, businessman, celebrity, and he likes a show, as does America, which is famous for its ticker-tape parades and all that sort of thing.

“It will be ebullient and positive and Trumpian. it will gold-plated and that's Trump. That's what he likes.”

But away from the razzmatazz and blood and sweat of the gargantuan gladiatorial display, it’s likely Trump, who like Thatcher is said to need just four or five hours of sleep a night, will start his day away from the cameras surrounded by his beloved family.

“We know he’s famously teetotal, so he won't be popping champagne or doing keg stands (drinking from a beer keg),” said Jennifer Ewing, spokeswoman for Republicans Overseas UK, “He loves a Diet Coke, and I wouldn’t be surprised over the years if he’s gotten a free Happy Meal on his birthday through his favourite restaurant McDonald's.

“I think he likes to celebrate and do it in a big way and have family and friends around.

“He’s famously close with his grandchildren, like many people at his age… and he does like to make a very big deal out of his birthday. He will not be having a lie in.”

Ms Ewing, who is an anti-war Republican, said one of Trump’s birthday wishes is, of course, “Make America Great Again”, but his other reported wish for “peace” was a “bit rich”.

Away from the fighting in the ring in Washington tonight, a real war is still raging between the US and Iran in the Middle East, causing inflation and soaring fuel prices for ordinary Americans and the rest of the world.

“If one of his birthday wishes was not peace, then maybe it wouldn't be as noticed… and people are like ‘well, maybe you shouldn't have bombed Iran in February’, that is a fair criticism of the president,” she added.

“His birthday wish, won't surprise anybody, is to, and I quote, “Make America Great Again”.

“He also mentioned that he wants peace, but as an anti-war part of the Trump coalition myself, I think that's a bit rich considering what's going on in the Middle East at the moment.”

But despite voter grumbles over more wars, Ms Ewing said she believes the spectacle of the UFC fight will still play well to Trump’s core support of “younger age men, aged 18 to 34”.

And she said criticism of extravagant events by leaders will “always” happen both in America and across the pond in Great Britain.

She said: “You will always have people saying, ‘hey, I can't afford to put groceries on the table and King Charles is riding around in a golden carriage'.

“You will always, whether it's a Republican or Democrat president, see people in the United States being critical of the money that's spent around the office.”

But Ms Ewing joked: “I’m not a royal commentator but I think some people might take offence (if King Charles had UFC fight staged outside Buckingham Palace).

The sporting spectacle is not being paid for by the American taxpayer, and TKO, the parent company, is said to be shelling out around £45 million for the right to stage the event on the South Lawn. TKO owner, Dana White, will join the president in watching the festivities tonight, along with invited US military veterans and serving servicemen and women.

Organisers expect a 120,000-plus crowd surrounding the White House who will watch the show on large screens after winning tickets in a lottery.

Trump’s birthday falls on Flag Day, which marks the date when the United States Congress officially adopted the Stars and Stripes as the symbol of the nation. It’s also just a few weeks away from America celebrating its own ripe old age of 250 years since it came into being on July 4, 1776.

Speaking about the advancing years of the country’s second president to reach his 80s in office, Ms Ewing said she was not concerned about his ability to do his job but noted he had become a “more exaggerated” version of himself, and “he swears a lot more”.

She said: “From a medical standpoint, the president has passed the Montreal Cognitive Assessment, it's called the MOCA, three straight times in a row, so doctors have ruled out any abnormalities or any signs of dementia.

“That aside, if you listen to the president and you compare him to, let's say, 10 years ago, 2016 when he first got into office, I think what you're seeing right now is a more exaggerated way of what he always was.

Sir Jacob agreed that Trump is still “compos mentis” despite reaching his 80th birthday and said, unlike when Joe Biden showed symptoms of decline, there is “no obvious change” in Trump. He said: “I was sent a clip from my daughter where he (Trump) was very rude to a lady from CNN, but he's always been very rude to ladies from CNN."

He added that with President Biden, towards the end, it was “obvious that he wasn't all there”, but that: “I don't think that's true of Trump.

"I think the same belligerent, decisive Trump is there, but that remains deeply puzzling to British voters who aren't used to that, and have a different temperament, a gentler personality than the American voter.”