More than a dozen senior Conservative MPs and peers have written to the prime minister calling for the UK to immediately recognise Palestine as a state, breaking ranks with their own party to do so.
Seven MPs and six members of the House of Lords have signed the letter to Keir Starmer urging him to defy the Israeli government and give formal recognition to Palestine in advance of key UN talks next month.
The letter, which has been seen by the Guardian, was written in late March soon after Israel broke its peace agreement with Hamas, diminishing hopes of an eventual two-state solution. On Monday, the Israeli cabinet went one step further, approving a plan to "conquer" the Gaza Strip and occupy most if not all of it.
In the letter, which was organised by the former minister Kit Malthouse, the group writes: "For decades, the Palestinian people have endured occupation, displacement and systemic restrictions on their basic freedoms.
"Recognising Palestine would affirm our nation's commitment to upholding the principles of justice, self-determination and equal rights. It would send a clear message that Britain stands against indefinite occupation and supports the Palestinian people's legitimate aspirations."
The letter continues: "Recognition should not be treated as a distant bargaining chip but as a necessary step to reinforce international law and diplomacy. Prime minister, we stand ready to offer our public support for this decision.
"This is an opportunity for Britain to show leadership, to be on the right side of history and to uphold the principles we claim to champion. More than 140 UN member states have already recognised Palestine - it is time for the United Kingdom to do the same."
The letter was signed by several on the moderate wing of the party such as Malthouse himself, the father of the house, Edward Leigh, and Simon Hoare.
But it was also signed by several associated more with the right, including John Hayes and Desmond Swayne. Members of the Lords including Hugo Swire, Nicholas Soames and Patricia Morris, the party's deputy speaker in the upper chamber, also signed.
The prime minister is understood not to have replied.
Most UN countries formally recognise a Palestinian state, but the US and most European countries do not. France and Saudi Arabia will co-host a conference next month designed to boost support for a two-state solution, at which the French president, Emmanuel Macron, has suggested France may grant formal recognition for the first time.
David Cameron, the former prime minister and foreign secretary, made a key concession last year when he said he wanted to see Palestine recognised as part of peace negotiations with Israel, rather than at the end of them.
A Conservative spokesperson said: "Our longstanding position has been that we will recognise a Palestinian state at a time that is most conducive to the peace process. We are not at that point now and we are clear that recognition cannot be the start of the process."
Starmer has used similar language, with the British government keen not to get too far ahead of the US. But David Lammy, the foreign secretary, said last week the government was in talks with France about its plans for next month.
"We have always said recognition is not the end in itself, two-states is the end in itself," he said. "We would prefer recognition as part of that process towards two states so we will continue to talk to partners about that."
Downing Street did not respond to a request for comment.