The British government is preparing to publish a summary of its legal advice stating there are no clear risks that selling arms to Israel will lead to a serious breach of international humanitarian law (IHL).

In a pre-prepared concession to the business select committee, the deputy foreign secretary, Andrew Mitchell, said: “In view of the strength of feeling in the IHL assessment process, I will look to see what more detail we could offer in writing on the IHL assessments in relation to Israel and Gaza both in process and substance.”

The government has so far rigidly insisted it will not publish any legal advice or any summary. It is not clear how much detail Mitchell has in mind but the release would follow a lengthy submission by the Foreign Office to the high court and a US decision to publish details of its thinking.

Mitchell caused incredulity among some of the MPs when he said the UK government does not believe “the significant military operation” in Rafah in Gaza has started, even though he admitted 800,000 Palestinian have chosen to flee the refugee city, half of them due to direct warnings from the Israel Defense Forces (IDF).

Mitchell has previously said he has seen no Israeli plan for Rafah that protects civilians, and indicated the government would oppose any operation without such a credible plan.

But Mitchell said the mass enforced displacement would not lead the government to change its assessment of Israel’s compliance with IHL. Instead, he said: “The government was seeking to take care of those displaced in the best way it could.”

During 90 minutes of cross-examination, the most sustained grilling a minister has faced on the issue, Mitchell repeatedly referred back to a decision made by ministers on 8 April that no risk of a serious breach of IHL existed.

Mitchell also for the first time confirmed that the 8 April assessment that no serious risk of a breach of IHL exists only included evidence taken up until the end of January, so any actions the IDF may have taken over four months have not been taken into consideration.

The UK has said it reviews its assessment of Israel’s actions on a rolling six weekly basis, which means a fresh assessment should have been published by ministers on Tuesday. No updated assessment has been announced and none of the MPs asked the minister when it would be announced.

In one exchange, Mitchell said: “You cannot use starvation as a weapon of war and remain within humanitarian law, that is clear.”

He was then asked by the committee chairman, Liam Byrne, whether people were dying due to lack of access to aid. He replied: “Whether or not that was my assessment would not directly affect judgments on international humanitarian law because the question is on issues of compliance, commitment and capability.”

He added he was “extremely worried by the position of children and everyone really” and that “the position in the hospitals are absolutely terrible”.

The business minister, Alan Mak, also said he would publish on 7 June updated figures showing the value of arms export licences granted between 7 October – the date of the Hamas attack on Israel – and the end of May.

He admitted that the government was three months late in publishing data on arms exports.

He said the presence of lawyers embedded in the Israeli army’s decision-making process was an important pointer to its intention to comply with the law.

David Cameron, the foreign secretary, rounded on the international criminal court in the Lords, saying its decision to seek arrest warrants for the Israeli prime minister, Benjamin Netanyahu, was mistaken in terms of timing, position and effect.

He repeated the view that the UK believes the ICC has no jurisdiction.

The comments came as the PCS union claimed that dozens of civil servants are seeking to escalate possible legal action against the government, which will allow them to avoid helping to arm Israel.

The head of PCS union said that members in the Department for Business and Trade are concerned that they may be culpable in acts of genocide in Gaza if they assist in issuing arms licences.

The clamour for legal action has increased since the chief prosecutor of the international criminal court said he is seeking arrest warrants for senior Hamas and Israeli officials for war crimes, a spokesperson for the union said.

“Given the ICC’s pursuit of Israel’s leaders, dozens of staff are now concerned that they are being asked to break international law,” the spokesperson said.

Fran Heathcote, the general secretary of the PCS union, said: “Our members in BEIS London South Branch and the newly formed DBT Department, that are responsible for arms licensing, brought this issue to the union’s attention and raised concerns that the British Government may be culpable in acts of genocide.

“We are currently in talks with our lawyers to explore a potential judicial review to halt this work in its tracks.”