Dominic Raab, the UK foreign secretary, is “incandescent with rage” at the US government’s refusal to grant the extradition of Anne Sacoolas, the wife of a US diplomat charged with causing the death of 19-year-old Harry Dunn in a crash in August, it has been claimed.

The family’s spokesman, Radd Seiger, made the claim after meeting Raab on Monday with Dunn’s parents, including his mother Charlotte Charles. Seiger said he was astonished at Raab’s anger.

He said the encounter had convinced him Raab was not going to brush the issue aside when he meets the US secretary of state, Mike Pompeo, on Wednesday in London. Seiger said: “He was incandescent with rage. On a very human level, he is a parent himself, and he made it clear that he is going to tell Pompeo that Sacoolas has to come back. He looked the parents in the eyes and said he was going to demand the return of Anne Sacoolas.”

Timeline Harry Dunn death Show 19-year-old Harry Dunn is killed following a collision involving Anne Sacoolas, the wife of a US intelligence official. Sacoolas is believed to have been driving on the wrong side of the road when she hit the teenager riding on his motorbike outside RAF Croughton in Northamptonshire. She cooperates with police at the scene and is breathalysed. However, this first account is not treated as an interview under caution. Officers visit Sacoolas’s address, where she provides an account of events and says she had diplomatic immunity. Northamptonshire police apply for a waiver to render this void. The US embassy notifies the FCO that the spouse of a member of staff at RAF Croughton has been involved in an accident. Specially trained liaison officers are embedded with the Dunn family, including parents Charlotte Charles and Tim Dunn, and Northamptonshire police’s investigation continues in the belief they cannot detain Sacoolas. The US asserts that Sacoolas is covered by diplomatic immunity. The Foreign Office formally asks the US embassy to waive immunity. The FCO is informed by the US embassy that it will not waive immunity and she will be leaving the country, unless the UK has strong objections. However, the foreign secretary, Dominic Raab, immediately objects in “strong and clear terms”. Sacoolas leaves the UK on a US Air Force plane. The FCO approaches the US embassy and is informed Sacoolas has departed. It immediately notifies Northamptonshire police that the waiver has been declined and Sacoolas has left the UK. Officials ask police to delay telling the family by up to two days so it can decide next steps. Five days after their son's funeral, the Dunn family inform the liaison officer they have been made aware of a suggestion that Sacoolas has left the UK. Police confirm this is true. Police meet the Dunn family to officially confirm Sacoolas’s departure, and officers go through what they know. Dunn’s parents visit the White House following an invitation by US president Donald Trump. He surprises them by telling them that Sacoolas is waiting for them in an adjoining room and wishes to meet them. They decline to meet her. Harry Dunn’s father confronts the foreign secretary in his constituency, where he encourages people to vote Raab out. Video footage of the encounter emerges showing Dunn politely approaching Raab as he arrives for the hustings. The politician claimed he was happy to meet but then dismissed Dunn, adding: “Not right in front of the cameras, it’s not on.” Dunn’s family launch legal action against the Foreign Office which they said could cost them “upwards of £50,000”. Tim Dunn issues a stinging attack on Raab, accusing the foreign secretary of “empty words” and only meeting the family as a publicity stunt. “We think politicians should be honest and decent, and we feel Mr Raab is neither of those,” he writes. The Crown Prosecution Service confirms it will start extradition proceedings after Sacoolas confirms she will not return to the UK to face the charge of causing death by dangerous driving The US state department describes the extradition request as “highly inappropriate”. A department spokesman said: “The use of an extradition treaty to attempt to return the spouse of a former diplomat by force would establish an extraordinarily troubling precedent.” Home Secretary Priti Patel is informed that US authorities will not grant the British government request to extradite Anne Sacoolas. The Home Office describedsthe decision by the US secretary of state, Mike Pompeo, as a “denial of justice”. Mattha Busby and Martin Belam

The thaw in the often frosty relations between Raab and the Dunn family has extended to an agreement that lawyers from both sides will shelve a costly proposed judicial review, and instead meet to discuss the Foreign Office’s initial handling of the case, including how it reached the view that Sacoolas, a wife of an intelligence officer at a US listening base in Northamptonshire, enjoyed full diplomatic immunity.

It appears Raab, previously described as cold by the family, convinced the Dunn delegation that he was genuinely animated by the US handling of the case.

Speaking to BBC Radio 4’s Today programme on Tuesday, Charles said: “The meeting went really well. You can see the anger in their eyes, faces, expressions and body language and they are definitely not happy at all that this extradition request has been turned down. They have given us concrete assurances they are looking at other ways to overcome the issue, and that they are doing the best they can to secure justice for Harry.”

Discussing her relations with the government, she said “there had been an awful lot of dialogue going on underneath the shouting, and we are getting somewhere. The relationship has gone from one of being very untrusting to very trusting. We have come a long way.”

Seiger said the Foreign Office was still looking at alternative options including a trial of Sacoolas in absentia in the UK or issuing an Interpol red notice, putting her at risk of arrest as soon as she leaves the US.

Seiger conceded there was still a dispute between the Foreign Office and the family over whether she had diplomatic immunity at the time of the crash. “What we agreed yesterday was to try to get the lawyers in a room to see if they can work that out. No one wants a court battle over this. We are all on the same page. Everybody wants that lady back.

“The Foreign Office says the issue of her immunity is not relevant and she should still come back, while we are very clear that issue should be resolved so we can say to Pompeo when he comes ‘you are simply wrong’, so that issue is still up in the air.

The statement issued by the Foreign Office after the meeting simply said Raab believed the Dunn family suffered a “denial of justice”, a phrase that has been used by Downing Street for the past few days. It argues that the issue of her diplomatic immunity should no longer be regarded as relevant.

Ministers are aware that they are facing a well organised campaign, and a deeply emotive issue, but also say that US conduct now means the whole issue of the US-UK extradition treaty has itself been brought into question.