Civil servants overseeing arms exports to Israel have requested to “cease work immediately” over fears they could be complicit in war crimes in Gaza.

Officials in the Department for Business and Trade (DBT) have raised concerns with senior civil servants that they may be liable if it is deemed Israel has broken international law.

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In correspondence seen by Sky News, the Public and Commercial Services Union (PCS), which represents civil servants, has requested an urgent meeting with the department to discuss “the legal jeopardy faced by civil servants who are continuing to work on this policy”.

The letter, sent on Wednesday, said: “Given the implications for our members we believe there are ample grounds to immediately suspend all such work.

“We therefore request that you meet with us urgently to discuss this matter and cease work immediately.”

The PCS confirmed to Sky News that it is considering legal action against the government,

The correspondence shows the union has been asking the government for its legal advice on arming Israel since January, when a preliminary ruling from the International Court of Justice (ICJ) found Israel’s acts in Gaza could amount to genocide.

A response to the union dated 13 March said “the question of criminal liability for civil servants is very unlikely to arise”.

However, the department said it can’t share the legal advice it is receiving as it is “confidential”.

Labour MP John McDonnell, a founding member of the PCS union group in parliament, said the government must “come clean”.

He told Sky News: “These civil servants should not be put at risk. The Rome Statute covering war crimes is clear that following a superior’s instructions is not a defence when it comes to charges of war crimes. The government must come clean on the legal advice they have.”

Paul O’Connor, head of bargaining at PCS, said: “They have put our members in the firing line, who have had to carry out things that are essentially in breach of not just domestic law but a whole raft of international obligations.

“With the situation unfolding in Gaza, there may be things that our members are asked to do which they know stands a very good chance of violating all manner of domestic and international law.

“They don’t want to be in a position where they’re being told to do things that are unlawful, particularly as the Civil Service Code obliges them to act in a lawful manner.”

Prime Minister Rishi Sunak has come under growing pressure to suspend arms sales to Israel after three British aid workers were killed in an airstrike on Monday.

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Last night, a letter signed by more than 600 lawyers, including former Supreme Court justices, warned the UK is breaching international law by continuing to arm Israel.

The government does not directly supply Israel with weapons, but does grant export licences for British companies to sell arms to the country.

The US remains by far the largest supplier of weapons to Israel, with Foreign Office minister Andrew Mitchell recently telling MPs that UK exports accounted for just 0.02% of Israel’s military imports.

There has been pressure within the Conservative Party to end exports – with MPs Flick Drummond, David Jones and Paul Bristow urging the government to reconsider.

The Lib Dems, the SNP and dozens of Labour MPs also want arms sales to be suspended, although the Labour leadership’s position is the government should publish its legal advice and suspend arms sales if there is a risk weapons could be used in “a serious breach of international humanitarian law”.

A government spokesperson said: “We keep advice on Israel’s adherence to International Humanitarian Law under review and will act in accordance with that advice.

“All export licence applications are assessed on a case-by-case basis against the Strategic Export Licensing Criteria.”