Ministry of Defence officials have privately accused a UK police force of wrongly handing over the investigation of an American fighter pilot who strangled a British woman to the US military, according to documents obtained by the Guardian.

Cambridgeshire police allowed the US military police to quickly take control of the investigation into Capt Jacob Wulfson after he had been accused of sexuallyassaulting Sarah Steele in his Cambridge flat.

The decision meant Wulfson was not tried in an English criminal court. Instead he was prosecuted in a military tribunal on a US airbase in neighbouring Suffolk.

Ministry of Defence officials said the Cambridgeshire force should “absolutely” not have let the US military police take over the investigation in a clear breach of a long-established agreement with the US.

The disclosure of the case by the Guardian in June provoked immediate criticism from Downing Street, which said it was “deeply distressing” and “very concerning” that the UK authorities were not involved in prosecuting Wulfson.

The government to set up a high-level inquiry to examine how and why police forces have been transferring investigations into serious crimes to the US military police.

The Ministry of Defence, which is responsible for handling the military relationship with the US, is one of the key departments taking part in the inquiry.

A batch of documents, disclosed via the Freedom of Information Act, revealed the private views of MoD officials about the Steele case, which centres on an obscure agreement signed by the US and the UK decades ago.

Under the terms of the agreement, police in the UK have the primary right to investigate alleged crimes by Americans stationed in the country.

The MoD officials made it clear the agreement was “pretty unambiguous” and only permitted the US military to acquire jurisdiction over investigations in a “narrow set of circumstances”. These circumstances are: if the offences were committed while the Americans were on duty, or if they were committed against another member of their armed forces or property.

In a memo written on 8 July, MoD officials based in Washington wrote: “The Steele case does not, on the surface, appear to meet the bar for a visiting force to be awarded jurisdiction.” In the agreement, the US military is formally known as a visiting force.

Four days earlier, the MoD officials had referred to the Steele case in an email to colleagues, saying: “The decision-making on this specific case seemed at odds with what is very clear” in the agreement.

Another MoD official agreed that “as best as we understand the facts, this should absolutely have been for the UK courts”.

An unidentified Greater Manchester police officer wrote in an email to MoD officials on 6 July that Cambridgeshire police had “wrongly, in my view” handed over the Wulfson investigation to the US military.

Cambridgeshire police said they were conducting a review of the case with what they called “the assistance of material provided” by US Air Force lawyers. The force said it “remained engaged with the victim”.

“We are working with government, wider policing and criminal justice partners to ensure greater clarity of jurisdictional decision making,” they added.

The US military aims to prosecute as many of its personnel as possible within the boundaries of its agreement with the UK.

The Americans often ask police in the UK if they can take over the prosecution of their military personnel – requests the police agree to, even when they have primary responsibility for investigating them.

A series of cases uncovered this year by the Guardian have highlighted concerns that British victims are required to give evidence in US courts martial, an unfamiliar legal system that often does not afford the same protections as that of a court in the UK.

Wulfson was off-duty when he assaulted Steele in his Cambridge flat in December 2023 after the pair talked on the Tinder dating app.

Steele testified at Wulfson’s court martial, which was held on his airbase at Lakenheath, Suffolk in April, that her experience was “degrading and distressing”.

The verdict and sentence were decided by an all-male jury of Wulfson’s fellow air force officers. All the lawyers were American. Steele was subjected to invasive and aggressive questioning by Wulfson’s lawyer.

Wulfson was convicted of strangling an intimate partner but acquitted of sexual assault. He was dismissed from the US Air Force and confined to a military jail on Lakenheath for six months.

The cross-government inquiry, which includes officials from the Home Office, Ministry of Justice and Foreign Office, is looking at how US military personnel are not being brought to justice in British courts.

The inquiry, which also involves police chiefs, is scrutinising a series of cases uncovered by the Guardian this year.

In each case, police handed over the investigations to US military police even though the American perpetrators were off-duty and the British victims had no connection to the armed forces.

They were tried in US courts martial on American bases. Tyrion Davis allegedly raped two women in Suffolk. He was convicted of one charge of sexual assault, but cleared of 10 further counts of sexual assault and abusive sexual contact.

Hannes Marschalek allegedly exposed himself to a 16-year-old girl and four young women in Littleport, Cambridgeshire. He negotiated a plea bargain at a court martial and admitted a charge of indecent conduct. He won an appeal in a US military court that quashed his conviction on technical grounds. This ruling is now being challenged.

The US has more than 12,000 US military personnel in the UK, stationed in at least 15 bases and facilities. The two biggest bases are at Lakenheath and Mildenhall, in Suffolk. Significant numbers of American military personnel live in East Anglia.