Israel's actions have been disproportionate and risk unnecessary loss of civilian life, said David Cameron and William Hague – not this week but almost exactly eight years ago.

The occasion was Israel's ground invasion of southern Lebanon, which resulted in more than 1,000 deaths. It appears that the Conservative leadership is once bitten, twice shy, following the backlash caused by those comments. "Not merely unhelpful but downright dangerous," was the verdict of the Tory donor Sir Stanley Kalms at the time.

It is a different conflict, but the dilemma remains over whether it is politically possible to criticise Israel's military actions without alienating those MPs, donors and voters whose backing for the country is unqualified.

The Labour leader, Ed Miliband, has taken the risk by condemning the incursion into Gaza as wrong and highlighting Cameron's "silence on the killing of hundreds of innocent Palestinian civilians". The Lib Dem leader and deputy prime minister, Nick Clegg, has matched Labour's position by branding Israel's actions disproportionate and gone a step further by calling for direct talks with Hamas.

Even the US has said Israel's recent attack on a UN school was "totally unacceptable" and "totally indefensible", urging "our allies to do more to live up to the high standards they have set themselves".

Philip Hammond, the foreign secretary, has said the situation in Gaza is "simply intolerable", but there has been no directly critical comment about Israel from any Conservative government minister. As for Cameron, he has so far limited himself to calling for an immediate ceasefire, while taking care to blame Hamas for sparking the crisis.

The mood on the backbenches is different. Pressure on Cameron to be bolder has come from several senior figures within his own party, including Margot James, a No 10 policy board adviser; Sir Peter Luff, a former defence minister; Crispin Blunt, a former prisons minister; Sir Nicholas Soames, the president of the Conservative Middle East Council; and Sir Peter Bottomley, another former minister.

On the other hand, there are still very many Conservative MPs who are firmly behind Israel's efforts to take out Hamas, while others are simply keen not to make any public statements on the issue, partly for fear of provoking the pro-Israel lobby.

"If you're looking for an explanation of why the government and many MPs have been quite so pusillanimous … go no further than the reaction to Hague in 2006, when he had temerity to call Israeli action disproportionate. There was opprobrium poured all over William," said one former Tory minister, who would like to see the government condemn Israel's shelling of Gaza but believes that is highly unlikely.

As for the US administration, it is probably being as "brave towards Israel as it's ever going to be" in terms of criticising its actions because Obama is in his last term in office, he points out. Cameron, with an election war-chest to raise and voters to win next year, does not yet appear willing to cross the same line.