The family of Harry Dunn are set to challenge the Foreign Office (FCO) over the diplomatic immunity given to his alleged killer in a High Court trial this summer.

The 19-year-old’s mother Charlotte Charles and father Tim Dunn are “looking forward” to seeing documents from the FCO which are due to dispute the claim that they had “no legal power” to advise Northamptonshire Police over the immunity granted to Anne Sacoolas.

The family will first face a case management hearing on April 3 – before a full trial at the High Court which the family spokesman, Radd Seiger, has said is likely to take place in June.

READ MORE: Family claim Foreign Office ‘cover-up’ over death of teenager

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

His alleged killer, 42-year-old Mrs Sacoolas – the wife of a US intelligence official who was based at RAF Croughton, claimed diplomatic immunity following the crash and was able to return to her home country, sparking an international controversy.

An extradition request submitted by the Home Office for Mrs Sacoolas, was rejected by US Secretary of State Mike Pompeo in January.

The PA news agency understands the FCO is set to employ Sir James Eadie QC to fight the parents’ claim – a lawyer who represented the Prime Minister at the Supreme Court in September last year during the row over the prorogation of Parliament.

Speaking on behalf of the family, Mr Seiger told PA: “Harry’s parents have brought a judicial review against the FCO and Northamptonshire Police.

“They wish to fully understand why they were treated so appallingly badly by the authorities following Harry’s death, who knew what and when, who tried to stop Anne Sacoolas if anyone from leaving the UK and to ensure that this never happens to another family again.

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“The FCO must set out the grounds on which it is resisting the Judicial Review and to disclose evidence in support by this Friday 6 March.

“Charlotte and Tim are looking forward to seeing these documents.

“It will be a small step towards getting justice for their son with court hearings coming on April 3 and the full trial now likely to place in June.”