British officials may now support the Palestinian United Nations bid in return for promises from President Mahmoud Abbas not to pursue Israel for war crimes and to resume the peace process.

Whitehall officials have said that Britain will vote “yes” on an upgrade for the Palestinian Authority to non-member observer status on three conditions, when the vote is held on Thursday.

The first condition is that the PA must not use its new status to join the International Criminal Court, a position some in Israel fear it would use to bring actions against Israel for alleged war crimes.

British officials also want an assurance that the PA will not then apply for full membership from the UN Security Council, and a commitment to returning to peace talks. President Abbas has previously said that he would like to use the UN upgrade to resurrect talks.

This news comes the day after reports that Liberal Democrat leader Nick Clegg was to lobby Prime Minister David Cameron and Foreign Secretary William Hague to back the bid.

A source told the Guardian newspaper: "Nick [Clegg] feels because they are going to be definitely doing it [applying], and clearly going to win the vote, it's important for us to vote for them to have observer status and not abstain."

Mr Clegg is understood to believe that British support for the more moderate PA led by President Mahmoud Abbas was even more important following the recent Gaza conflict.

This week’s bid is the next stage in a process that began with an unsuccessful application for full membership in September 2011. That bid did not go to a vote, as a veto from the US as a Security Council member was expected. It is expected that the motion will pass with a two-thirds majority, with or without Britain’s support due to backing from states in Africa, Latin and South America and the Middle East.