The parents of Harry Dunn have been given a personal assurance by the home secretary, Priti Patel, that extradition proceedings against Ann Sacoolas, the American charged with the death of the 19-year-old, will be influenced only by the law, and not politics.

Patel met members of the Dunn family at their home for nearly an hour and a half partly to set out the legal process ahead.

The Crown Prosecution Service announced on Friday that it had given Northamptonshire police permission to charge Sacoolas with causing death by dangerous driving, an offence that can carry a maximum 14 year sentence.

Dunn was on his motorcycle when he was hit by a car driven by Sacoolas on 27 August.

The Home Office has already said it will start what may emerge to be lengthy extradition proceedings.

Patel met Tim Dunn, Harry’s father, at his home for nearly 90 minutes in the company of their local MP, Andrea Leadsom. Harry’s mother, Charlotte Charles, did not attend the meeting.

The Dunn family were also told they would meet Boris Johnson early in the new year in Downing Street.

Sacoolas, in a statement issued by her lawyers on Friday, expressed remorse at causing Dunn’s death, but said she would not return to any criminal proceedings in the UK, citing among other things the potential length of her sentence.

The lawyer said: “This was an accident, and a criminal prosecution with a potential penalty of 14 years’ imprisonment is simply not a proportionate response.”

Sacoolas has been given the support of the US state department, which described the CPS decision as unhelpful. US officials have been negotiating to see if the Dunn family would allow the Sacoolas family to help provide a memorial for their son, as well as training to prevent such accidents reoccurring.

Sacoolas had been in the UK for only a matter of weeks and was driving on the wrong side of the road when the collision happened. Signs have now been put up at the RAF Croughton base where her husband worked as an intelligence officer reminding drivers of the British driving rules.

Speaking after the meeting, Radd Seiger, a spokesman for the Dunn family, said: “We feel incredibly reassured that this whole saga will be dealt with under the rule of law.”

Leadsom, who is also the business secretary, said: “It’s been fantastic to bring the home secretary, Priti Patel, to come and see Harry’s family.

“They seemed to be quite reassured that Priti has set out what the next steps are and I do think that will be able to give them a little bit of relief temporarily while that process continues. I’ve assured Harry’s family I will do everything I can to get justice for Harry.”

Patel said she was “very grateful” to the family for meeting her during such a difficult and traumatic time.

She added: “It was a nice opportunity to hear from them, obviously about what they have been experiencing, what they have been going through, and to reassure them at what has been a very difficult and traumatic time for them.”

The prime minister is politically close to Donald Trump, and will be putting pressure on the White House to drop its refusal to let Sacoolas to return to the UK.

On a visit to Estonia to see British troops, Johnson said the government was still trying to bring its pressure to bear.

“The law should take its course and we’ll be following the case with keen interest and continuing to make representations on behalf of Harry Dunn’s family in the US at every level,” he said.

The extradition process is in theory an entirely legal process. A state department lawyer looks at the request and assesses whether it conforms to the 2003 treaty that underpins extradition between the two countries.

The key test set out in the treaty is that the British request must include “such information as would provide a reasonable basis to believe that the person sought committed the offence for which extradition is requested”.

The US justice department also examines whether there is “probable cause” to justify the request.

This test comes from the fourth amendment to the US constitution, which states that people cannot be arrested unless the authorities have “probable cause” for their action. Although there are many cases pending, there is no case so far under the treaty by which an extradition request by the UK has been rejected by the US.

Anyone facing extradition has numerous appeals available to them in the US or the UK before they can be forced to return to the UK.