Israel is “flagrantly and regularly” committing war crimes in Gaza, according to a former British diplomat who recently resigned over ministers’ failure to ban arms sales to Benjamin Netanyahu’s government.

Mark Smith, who resigned as a counter-terrorism official at the British embassy in Dublin after raising complaints about the sale of British weapons to Israel, told the BBC on Monday that he believed Israel to be in breach of international law.

Smith told Radio 4’s Today programme: “When you look at what constitutes a war crime, it’s actually quite clear, even from what you see in open source on the TV, that the state of Israel is perpetrating war crimes in plain sight.

“Anybody who has a kind of basic understanding of these things can see that there are war crimes being committed, not once, not twice, not a few times, but quite flagrantly and openly and regularly.”

Smith’s exit became public over the weekend after a resignation email was leaked in which he accused senior members of the Israeli government of “open genocidal intent”. In a message that was sent to hundreds of officials and advisers, Smith said there was “no justification for the UK’s continued arms sales to Israel, yet somehow it continues”.

The resignation came as the British government carries out a review of its export licensing rules for arms to Israel. David Lammy, now the foreign secretary, called in opposition for a “pause” in sales but since taking office has said he is looking at curbs on “offensive weapons in Gaza”.

Lammy’s review has been delayed because of the widening Middle East crisis and because of the legal difficulty in distinguishing between offensive and defensive weapons.

While that review goes on, lawyers have submitted claims to the high court in London of Palestinians being tortured, left untreated in hospital and unable to escape constant bombardment. The lawyers are seeking a court order blocking further arms sales because of what they say is a clear risk that the weapons would be used to commit breaches of international humanitarian law.

Weapons manufacturers seeking export licences to sell to Israel say they have been told that new licences have been suspended pending the review.

Smith, who says he previously led a government assessment of the legality of arms sales to different countries, said on Monday he had raised his concerns with the foreign secretary and at “pretty much every level of the organisation”.

Asked what response he had been given, he replied: “I resigned because of this issue, so you can put the pieces together. But suffice to say that any response was not satisfactory.”