Boris Johnson has said the chances of the US handing over Anne Sacoolas, the woman suspected of causing Harry Dunn’s death in a car crash, are “very low”.
However, the prime minister has said his government has made an extradition request and will “make every effort” to secure justice for the teenager’s family.
Sacoolas left the UK after the car she was driving hit Mr Dunn’s motorbike outside RAF Croughton in Northamptonshire in August.
Speaking to BBC Breakfast, Mr Johnson was pressed on whether Sacoolas would be forced to return to the UK.
He said: “I think it’s right that we have made the appeal and I have to be clear, I think the chances of America responding by sending Anne Sacoolas to this country are very low. It’s just not what they do, but we will continue to make every effort we can.”
In December, Sacoolas was charged by the Crown Prosecution Service with death by dangerous driving.
But the US has maintained that Sacoolas had immunity at the time of the incident and that extraditing her “would establish an extraordinarily troubling precedent”.
Responding to the PM, Radd Seiger, the Dunn family spokesman said: “I do not know what is in the Prime Minister’s mind in making those comments because the parents and I have not yet had the opportunity to sit down and talk with him – but we expect to do so within the next few days.
“Certainly, if he is basing those comments on what is currently emanating from Washington he may well be right.”
But he added that “my analysis of the prospects of success are diametrically opposed to Mr Johnson’s”, following discussions.
He said: “But we will take one step at a time and not get ahead of ourselves. Anne Sacoolas will be coming back to the UK to face justice. Unlike the Prime Minister, there is no doubt in my mind.”
Elsewhere in the interview, Mr Johnson said he is “absolutely confident” that the Royal Family will resolve the issues surrounding Harry and Meghan stepping back – and would do so “much more easily without running commentary from politicians”.
Asked about whether media intrusion was a factor, Mr Johnson said: “Everybody has got an opinion but it doesn’t mean the problem is helped by politicians weighing in.”
The prime minister also declined to answer questions about whether race had played a part in the coverage of Meghan joining the Royal Family.
On Brexit, Mr Johnson said it was “very likely” that there would be a trade deal by the end of the year, adding later that it was “epically likely”.
However, he warned the government would have to prepare for a scenario where a deal is not reached.
Mr Johnson added that the UK would rediscover how it built itself up, saying: “Free trade has done more to lift billions of people out of poverty than anything else and that is why I believe in it.
“We can do fantastic deals not just with the EU but with countries around the world and that work begins on 1 February.”
On whether Big Ben should chime at 11pm when the UK leaves the EU, he said the “bongs” would cost £500,000, so they would be costly.
He said: “We are working up a plan so people can bung a bob for a Big Ben bong. I haven’t quite worked it out.
“But Big Ben is being refurbished and they seem to have taken the clapper away so we need to restore it, but that is expensive.”
Asked about whether he would be a different Boris Johnson in 2020 – and stop stunts where he is a “submarine lurking below the surface” – he said: “The submarine is crashing through the iceberg. Here I am right now.
“I want to be as available as I possibly can. But I do believe in cabinet government.
“I want them to be leading. For example, the secretary of state for Northern Ireland did a good work in getting Stormont up and running.”
The prime minister said the NHS was “our number one priority”.
Mr Johnson claimed he would fund the NHS with the “biggest ever cash injection” and promised “50,000 more nurses” – a number which was repeatedly said to be incorrect during the election campaign because it includes retention of current nurses who may have left.
He said: “We will build new hospitals, we will do upgrades. This is a massive project which requires a revolution in the way we do medical care and social care.”
Mr Johnson also said his proposal on social care would be brought forward, and claimed that governments have been shirking this issue for 30 years.
He said it would be done “in this parliament”, but refused to specify when – later clarifying he would bring a plan this year and carry it out by the end of his five-year term.
On Flybe, the prime minister said it was not for government to step in and save businesses in trouble, but he did see the importance of the network in regional connectivity.
Mr Johnson said they were “working very hard but there are limits commercially to what a government can do”.
He added: “But we will ensure there is regional connectivity that this country needs.
“That is part of our agenda of uniting and levelling up. We don’t have good enough infrastructure.
“People don’t feel they have a chance to get to the opportunity areas.”
The prime minister was also asked about Huawei’s potential involvement in the UK’s 5G infrastructure, after the US reportedly warned that using the Chinese company’s technology would be “nothing short of madness”.
He said: “The British public deserve to have access to the best possible technology.
“We want to put in gigabit broadband, but if people oppose one brand or another then they have to tell us what’s the alternative.
“I don’t want as the UK prime minister to put in any infrastructure that would compromise our security or ability to co-operate with Five Eyes intelligence.”
Mr Johnson was also asked when the Russia report would be released, which investigated the country’s interference in UK politics.
He said: “I don’t know when it will be published but there’s no reason it shouldn’t be.
“I happen to have read it, and I think after all that clamour in the election campaign people will be disappointed.”