Philip Hammond, the foreign secretary, has taken the highly unusual step of criticising a high court judge’s decision to strip diplomatic immunity from a Saudi billionaire facing divorce proceedings from his estranged wife.

Last month Christina Estrada, a former Pirelli calendar model, won the right to fight for a share of Sheikh Walid Juffali’s £4bn fortune. The couple split up following 13 years of marriage.

At the high court, Justice Anthony Hayden dismissed as “spurious” the Saudi businessman’s claim to have been shielded from litigation because of his role as permanent representative to the International Maritime Organisation (IMO) for the tiny Caribbean island of St Lucia.

Christina Estrada can now fight for a share of her husband’s £4bn fortune. Photograph: Rex/Shutterstock

However the Foreign Office said that if the decision stood, British diplomats could be hauled before the courts of any country in which they are serving and their position “scrutinised, and their status unjustifiably curtailed”. Hammond bluntly said the high court’s ruling “should not be upheld or endorsed”.

In the Juffali case, the judge decided that he had “no pre-existing connection to St Lucia” and there was no evidence that he “has any knowledge or experience of maritime matters”. He said the Saudi businessman only sought to become a diplomat to defeat “[his wife’s] claims consequent on the breakdown of their marriage”.

Juffali’s role as a diplomat, said the judge, was “an entirely artificial construct”, adding the sheikh “has not, in any real sense, taken up his appointment, nor has he discharged any responsibilities in connection with it”.

Juffali, who chairs one of Saudi Arabia’s largest companies, sought to reverse the judgment in the court of appeal. He said the decision was “deeply offensive, not least in its conclusion that his appointment … is an artifice”. The judgment is expected this week.

Philip Hammond said it was the decision of the Foreign Office whether to accept someone as a diplomat or not. Photograph: Ben Pruchnie/Getty Images

In an unusual step, the Foreign Office submitted an opinion from Tim Eicke QC backing the Saudi billionaire. It said the judge had made a mistake in attempting to decide whether Juffali had been a diplomat.

In the evidence, Hammond said the “judge erred in concluding that it was necessary (or permissible) for the court to ‘look behind’ the Foreign and Commonwealth Office certificate, which confirmed that [Juffali] had been appointed to the post of permanent representative of St Lucia to the IMO and to consider whether (he) had taken up the post or exercised any functions in connection with it”.

The cabinet minister argues that only the “executive (acting through the FCO) as part of the royal prerogative of conducting foreign relations” can decide to “accept (or not) a diplomat”.

The intervention by the foreign secretary is significant because a growing number of litigants are claiming diplomatic and state immunity in English courts, with lawyers saying that the capital is attracting a global super rich partly drawn to London as a good place to fight legal disputes.

About 22,000 people are entitled to diplomatic immunity in Britain – this includes diplomats and their families. Last month the high court ruled that one of the world’s richest men – Sheikh Hamad bin Jassim bin Jaber al-Thani, the former prime minister of Qatar – could not be sued in London over claims that agents acting on his behalf falsely imprisoned and tortured a British citizen, because he is protected by diplomatic immunity.

In that case, Hammond’s deputy, James Duddridge, said that “it is ultimately for the court to decide whether a foreign diplomat in the UK enjoys immunity in any particular case”.

Geoffrey Robertson QC said diplomatic immunity was putting diplomats ‘above the law’. Photograph: Peter Macdiarmid/Getty Images

Geoffrey Robertson QC, a former UN judge, told the Guardian that UK courts should have the power to rule on diplomatic immunity to stop “sham” appointments being made by foreign embassies and end “abuse” of the law by rich and powerful individuals.

Robertson said that the abuses of diplomatic immunity have grown in parallel with the rise of human rights law. “Take for example the idea that everyone should have access to a court. So we are seeing cases where a rape victim can’t have access to the court because the alleged rapist is a diplomat. So this immunity destroys our rights to access to justice which comes from the Magna Carta.”

What diplomatic immunity does, says the QC, is put diplomats “above the law”. He said: “One of the most marked cases is that diplomats are not allowed to engage in business and we know Middle Eastern embassies where they do little else. The government has turned a blind eye to this because the Foreign Office favours certain governments for trading reasons and doesn’t ask questions. Until now the courts have said ‘well the UK government accepts these people as diplomats and diplomats they are’. That might be changing.”

The Foreign Office did not respond when contacted by the Guardian.

