The general secretary of Britain’s biggest union has written to supporters of Israel to defend comments he made during Operation Pillar of Defence.

Unite had issued a statement signed by Len McCluskey six days into the violence between Israel and Hamas in November. It “unreservedly condemned outrageous Israeli aggression” and accused Israel of “terrorising an entire population”.

The statement claimed the conflict had followed “the illegal Israeli assassination of Palestinian leaders in Gaza”, but made no mention of the thousands of terrorist rockets fired on Israeli civilians in the preceding decade.

The We Believe in Israel advocacy group encouraged supporters to write to Mr McCluskey to complain about the “one-sidedness” of the statement. Around 200 people did so.

In a response sent last week to those who had complained, Mr McCluskey said he had been “taken to task for a variety of what are in reality, imagined or contrived, offences” and said Unite remained “wary” of Hamas, partly due to its expulsion of the Palestinian General Federation of Trade Unions.

But he followed that with a series of further allegations against Israel dating back to 1967 and concluded: “The strength of opinion among British trade unionists is such that they will not stand idly by when the combined weight of IDF weaponry rains down on a largely defenceless and undefended people in Gaza.”

Unite took a lead, he said, from pro-boycott campaigner Archbishop Desmond Tutu, who has accused Israel of apartheid.