Sadiq Khan has broken ranks with Sir Keir Starmer and demanded a ceasefire in Gaza, heaping fresh pressure on the Labour leader to reverse his stance.

The Mayor of London issued a statement calling for his party to back a truce and openly criticise Israel, which he suggested was breaking international law.

His intervention will add fuel to growing public and private clamour from Labour frontbenchers and MPs for the party to drop its defence of Tel Aviv’s military response.

It caps one of Sir Keir’s toughest weeks as the Labour leader, in which he has faced a full-scale revolt on his stance that Israel has the right to defend itself in Gaza.

Mr Khan had remained conspicuously silent on the issue until Friday morning, when he split with the party leadership to demand that it advocates for a truce.

In a video message, he said: “I join the international community in calling for a ceasefire. It would stop the killing and would allow vital aid supplies to reach those who need it in Gaza.

“It would also allow the international community more time to prevent a protracted conflict in the region and further devastating loss of life.

“A widespread military escalation will only deepen the humanitarian disaster. It will increase human suffering on all sides.

“No nation, including Israel, has the right to break international law.”

Sir Keir has come under increasing public pressure throughout the week, including from his own shadow cabinet, to reverse his stance and support calls for a ceasefire.

Ceasefire advocates should ‘grow up’

So far he has supported the Government’s response to the crisis, including by backing the idea of “humanitarian pauses” to allow aid in and people out of Gaza.

He has won some plaudits for standing firm and for ensuring that Britain projects a united response in support of Israel as it faces down Hamas terrorism.

Lord Blunkett, a Labour former home secretary, accused those calling for a ceasefire of trying to “make themselves feel better” and said they should “grow up”.

He told the BBC: “I’m talking about some of my colleagues who think it’s more important to make a gesture than it is to stay together and have a very clear view of all of this.”

Lord Austin, a former minister who quit Labour because of its “culture of anti-semitism” under Mr Corbyn, meanwhile hit out at the Mayor of London for his intervention.

He said: “Sadiq Khan can’t stop kids killing each other on the streets of London, yet thinks he can provide useful advice on the most complicated and difficult conflict in the world.”

Sir Keir’s position has been dismissed by many Labour MPs as not going far enough, with many reporting huge levels of anger among Muslim voters in their seats.

Backbenchers have been offered extra security advice after some were targeted by local campaigns branding them “traitors” and “backstabbers”.

Left-wing MPs renewed their opposition to the leadership’s stance in light of Mr Khan’s statement, saying that it showed Sir Keir had to change his position.

Beth Winter, the MP for Cynon Valley, said: “Welcome to see Mayor of London give voice to the public demand for a ceasefire in Gaza – to end the further devastating loss of life.”

Humanitarian pause ‘not good enough’

Marsha de Cordova, the MP for Battersea, said: “Sadiq Khan is right. I will continue to back calls for a ceasefire, only a political resolution will lead to peace for Palestinians and Israelis.”

On Friday, Jeremy Corbyn, the former leader who remains a popular figure amongst those on the Left of the party, also openly attacked Sir Keir’s stance.

He said: “A humanitarian ‘pause’ is not good enough. How long should Palestinians be given to mourn the dead before the bombs restart? We need a ceasefire now.”

More than one in five Labour MPs, including frontbenchers, have publicly urged Sir Keir to reverse his stance and at least half the party’s MPs are said to privately back a truce.

Steve Reed, the shadow environment secretary, said that he could “completely understand and empathise with colleagues” but defended the Labour leadership’s position.

He said if Britain had been attacked in such a way that “our state would have sought to defend ourselves … by dismantling the capability of a terrorist organisation that carried it out”.

The frontbencher also insisted that Sir Keir’s stance would not affect the party’s chances of winning the next election amid reports of a collapse in Muslim support.

“In politics, you should do the right thing, not the electorally expedient thing,” he told Sky News.