'You need to stop apologising,' says Warren Stephens, American ambassador to the United Kingdom. A year into the job, he is very familiar with our national tendency to say 'sorry'.

But he sees no reason to play down our nation's past.

'I tell my British friends that if you look at the vast majority of your former colonies, they are doing pretty damn well. That's because of you,' he says, echoing Donald Trump's recent speech on the values and systems which the US absorbed from the colonial motherland.

'One of the greatest lines that I've heard was when the President said: 'It was the greatest inheritance one nation could give another'. It's absolutely true.'

It is certainly not the only area in which Mr Stephens believes we are underselling ourselves. He talks up Britain in a way we seldom hear from many home-grown public figures as he points to our natural and human resources. 'Not taking advantage of your fossil fuel reserves seems to me to be the crux of the issue. I really do not understand the reluctance to do it,' he says.

Having only just got to know ministers here in Britain, he says he will be 'sad' if he has to say farewell to Sir Keir Starmer. 'We'll work with whoever is in Government,' he says, adding that he has yet to meet Andy Burnham.

'I've spent a year trying to get to know people in the current Government. If we start over, that just throws everybody back to square one.'

Mr Stephens is marking his first anniversary as Mr Trump's emissary to Britain with a trip to Sulgrave Manor in Northamptonshire. George Washington's ancestral family home is a pretty 16th-century mini-stately home built by the founding president's five-times great-grandfather. The house was bought by British and American well-wishers after the First World War and restored as a monument to UK-US friendship.

A student conference is taking place on the day Warren Stephens visits with his wife, Harriet. The ambassador gives them a thoughtful speech reflecting on our enduring bilateral ties. 'The 'Special Relationship' is a bit like a Hollywood actor,' he says. 'You couldn't pin its exact age if you tried.'

A keen scholar of history, Mr Stephens greatly enjoys a tour of the house, which still bears the Washington arms above the door – the same arms used today by Washington DC.

At Sulgrave, they sit beneath the Crown and 'ER' cypher of Queen Elizabeth I, a reminder that the Washingtons, like the nearby Spencer family, made their fortune in the Tudor wool trade – and were also die-hard royalists.

The royal connection surfaces during two interviews with Mr Stephens, one here and an earlier chat at the US embassy.

For Mr Stephens's arrival in London came ahead of a momentous run of events – including President Trump's state visit to Windsor eight months ago, the King's hugely successful state visit to the US last month and the upcoming 250th birthday of the USA on July 4. Amid all the razzmatazz, there have also been some tricky moments as President Trump has had some harsh things to say about British foreign policy, not least on the subject of Iran. Britain's initial refusal to let the US use RAF bases had repercussions.

'That upset the President – upset me. Our air crews had to fly 35-ish hours for the initial attacks and refuel I don't know how many times. That's a very dangerous manoeuvre. We lost a whole tanker crew to a refuelling accident.'

But he is quick to point out that 'everyone has moved on' and that relations are 'very, very solid'.

'We've always had disagreements and we will going forward,' he says. 'I think that's a great sign of a healthy relationship.' He points to our military, cultural, commercial and personal ties, epitomised by President Trump's deep affection for this country. 'Really, the President's fondness for the King, Queen, Royal Family and late Queen makes our job a lot easier.'

Mr Stephens, 69, comes to the role after a distinguished career running his family's investment bank in Little Rock, Arkansas.

Established by his father and uncle, Stephens Inc managed the share flotation for local shopkeeper, Sam Walton, following which Walmart grew into the largest retailer in the world.

As well as being a major benefactor to education and the arts in his home state, Mr Stephens has donated to several Republican campaigns over the years, including those of Mr Trump.

Last year, with his three children now at the bank, he was summoned to an interview with the President at Mar A Lago, after which he was offered a new job.

Mr Trump's announcement – via a post on Truth Social – is framed at his office at the new US embassy building in Vauxhall. Here, too, are portraits of two of Mr Stephens's great heroes, Sir Winston Churchill and President Dwight Eisenhower.

Also in pride of place are the medals and badges of Mr Stephens's grandfather who served in the First World War. His father, Jack, joined the US navy at the end of the Second World War (he was a naval academy friend of future President Jimmy Carter).

Mr Stephens well remembers his first trip to Europe as a boy in 1966, including a trip to the D-Day beaches in Normandy. 'There were still tanks and landing craft rusting out in the water.'

The most exciting part of the entire trip, he recalls, was riding on a London double-decker bus. 'That was all I wanted to do!' In adult life, he and Harriet came to know London extremely well and they were delighted last year to arrive at Winfield House, the famous US residence in Regent's Park.

One of his first duties was the formal presentation of credentials to the King at Buckingham Palace. By tradition, they arrived in a horse-drawn carriage after careful rehearsals of the precise ritual and words which new ambassadors are meant to recite. 'I was quite nervous but he put us at ease right away and said: 'Oh, I believe you have some papers for me?'

There was an equally memorable carriage procession not long afterwards as the President and the First Lady, Melania Trump, arrived at Windsor in September.

It was the first time a US president had paid two state visits and travelled in a carriage (the Secret Service had always forbidden such things on public roads so the King had laid on a private procession through the park).

Mr and Mrs Stephens followed in a carriage with the Prince and Princess of Wales. 'It was one of the many moments Harriet and I have had where we just pinch ourselves and say: 'Is this real?' Prince William said his grandmother always said it wasn't a proper state visit without a carriage ride. So the President got a proper visit.'

Because US ambassadors are, by tradition, presidential friends or appointees, rather than career diplomats, many have opted for a low profile and an easy ride. That was hardly an option for Mr Trump's man in London.

Mr Stephens is active on multiple fronts. He has been vocal in urging Britain not just to open up the North Sea but to get fracking. 'I want the UK to have the strongest economy it can have so it can be the best ally to the US. I'm not saying this to be preachy. I'm just saying there's a reason natural gas costs $3 an MCF [unit] in the US and $12-to-$15 here.'

Cosying up to the EU, he says, carries serious risk to the UK/US trade deal: 'The EU imposes an awful lot of onerous rules and regulations.' And he is quick to reiterate the President's demand for higher defence spending.

A particular worry is the undersea cable network linking the US and Europe. 'We think everything goes by satellite, and it just doesn't. That's an obvious weak link. If we can't communicate, we can't do anything. Sometimes old technology is the best.'

He is also maximising the US's presence in London. He has just negotiated a new 150-year lease on Winfield House (which needs some work done). When I meet him at the embassy, he has laid on an exhibition which includes Benjamin Franklin's bank statement and an original copy of the Declaration of Independence.

The ambassador points to its most famous line, 'We hold these truths to be self-evident…' As he observes: 'Franklin had heard [it] from one of the Scottish political philosophers. It's in the DNA. It's your DNA and our DNA. And it's pretty much inseparable.'