The mother of teenage motorcyclist Harry Dunn has issued a further plea to the Prime Minister and urged him “not to be frightened” of meeting her.

Charlotte Charles said she did not want to take Boris Johnson away from “important work” but insisted there were a number of “very serious problems” that needed addressing “for the benefit of the nation” following her son’s death.

The 19-year-old’s family have made numerous pleas to Mr Johnson for a meeting but no talks have ever taken place.

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Mr Dunn’s parents have met Foreign Secretary Dominic Raab on a number of occasions, but Mrs Charles has said their concerns are “not just an issue of diplomatic immunity for the Foreign Office to address”.

The teenager was killed when his motorbike crashed into a car outside a US military base in Northamptonshire on August 27 last year.

In a letter addressed to the Prime Minister, Mrs Charles wrote: “We have tried many times to get you to sit down with us, not because we want to take you away from your other important areas of work, but because we think that what happened to Harry has highlighted a number of very serious problems which need to be fixed urgently for the benefit of the whole nation.

“This is not just an issue of diplomatic immunity for the Foreign Office to address, as important as that is.

“Given what happened to Harry, the Department of Transport and the Department of Health and Social Care must get involved as well and we want you, as the person who wanted to become Prime Minister, to listen to our grave concerns personally so that you can lead from the front and pull a team together across government to address the problems.

“Your primary responsibility is to safeguard and protect our lives and your administration and those before yours have sadly failed to do so I’m afraid.”

Urging Mr Johnson to meet with them, Mrs Charles said: “I don’t know why you haven’t wanted to see us. Please don’t be frightened.

“Please meet with us so we can talk about and address the issues.

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“We mean no harm and just want to ensure that Harry did not die in vain.”

The suspect in the case, 42-year-old Anne Sacoolas, wife of a US intelligence official based at RAF Croughton, was granted diplomatic immunity following the crash and was able to return to her home country, sparking an international controversy.

An extradition request from the Home Office for Mrs Sacoolas was rejected by US secretary of state Mike Pompeo in January, which was described by the Prime Minister as a “denial of justice”.