The shadow foreign secretary has said it “seems unthinkable” Dominic Raab would not have been told of the Harry Dunn crash for almost two weeks after a briefing note about the death was sent to his private office.

Lisa Nandy said the emergence of a memo which detailed the issues surrounding the case, in court documents seen by the PA news agency, was “deeply concerning and raises serious questions about the Foreign Secretary’s account of events”.

On Wednesday, Foreign Office sources said Mr Raab was not made aware of Harry Dunn’s death until after September 12 – the day he attended a reception with US Ambassador Woody Johnson.

The briefing note – sent to the then-foreign ministers Heather Wheeler and Chris Pincher, and copied to Mr Raab’s private secretary – discussed the potential for some “very unpalatable headlines”.

Ms Nandy said the memo, dated August 30, “demonstrates a complete lack of respect to Harry and his family”.

The shadow foreign secretary said the explicit reference to ambiguity surrounding the diplomatic immunity claimed by suspect Anne Sacoolas “directly contradicts information provided to Northamptonshire Police by the Foreign Office” in the days following the crash.

Mr Dunn, 19, was killed when his motorbike crashed into a car outside a US military base in the county on August 27 last year.

Sacoolas, 42, the wife of a US intelligence official, claimed diplomatic immunity following the crash and was able to return to her home country.

She was charged with causing death by dangerous driving in December but an extradition request, submitted by the Home Office, was rejected by US secretary of state Mike Pompeo in January – a decision later described by the State Department as “final”.

The victim’s mother, Charlotte Charles, called for Mr Raab’s resignation on Wednesday – adding: “You wouldn’t treat an animal the way Government has treated us.”

Expressing her views on the memo, Ms Nandy told PA: “The emergence of a briefing note between senior Government ministers and the Foreign Office discussing the case of Harry Dunn is deeply concerning and raises serious questions about the Foreign Secretary’s account of events.

“Not only does this briefing note make explicit reference to the ‘ambiguity’ surrounding the diplomatic immunity of Anne Sacoolas – directly contradicting information provided to Northamptonshire Police by the Foreign Office in the days following the accident – but the discussion of ‘very unpalatable headlines’ demonstrates a complete lack of respect to Harry and his family.

“It seems unthinkable that the Foreign Secretary would not have been made aware of such an important diplomatic incident for almost two weeks after this briefing note was sent to his office.

“Harry Dunn’s family deserve answers to their questions and justice for their son, and these latest communications further demonstrate the need for a parliamentary inquiry into what happened in this case.”

The Dunns’ family spokesman, Radd Seiger, told PA: “As the internal memo dated August 30 shows, the most senior of (Mr Raab’s) aides in the Foreign Office were notified of the crash and the impending crisis.

“It is incredulous that they did not make the Foreign Secretary aware.

“To further suggest that he attended a function at the US Ambassador’s residence on September 12, with laughter and joy in the air, and that he was unaware that there was a crisis under way between the two countries and a family 70 miles away who were preparing their son’s funeral, raises serious questions.”

He added: “There is a totally innocent family on their knees here, who deserve our support.

“They are getting the opposite from this Government. Thank goodness for their millions of supporters around the country.”

A spokesman for the Foreign Office said: “We have the deepest sympathy for Harry’s family. No family should have to experience what they have gone through. The case remains of the highest priority for the Foreign Secretary who continues to raise the case with the US Government, including last week.

“Both the Foreign Secretary and the Prime Minister have been clear with the US that the refusal to extradite Anne Sacoolas amounts to a denial of justice, and that she should return to the UK.

“We are committed to revising the arrangements at RAF Croughton to ensure they cannot be used in this way again. The Foreign Secretary remains ready to meet Harry’s family and to support them to get the justice they deserve.”