Foreign Secretary William Hague is under pressure to back a historic vote at the United Nations granting recognition of a Palestinian state.
In a Commons statement, Mr Hague said Britain would only support the resolution at Thursday's meeting at the UN General Assembly in New York if the Palestinians gave a commitment to an immediate and unconditional return to the negotiating table with Israel.
He said the UK would also require an assurance that the Palestinians would not seek to extend the jurisdiction of the International Criminal Court (ICC) over the Occupied Territories.
"Up until the time of the vote itself, we will remain open to voting in favour of the resolution if we see public assurances by the Palestinians on these points. However, in the absence of these assurances, the United Kingdom would abstain on the vote," he said.
His comments drew a dismissive response from shadow foreign secretary Douglas Alexander who urged him to stop dithering and come out firmly in favour of Palestinian statehood. He warned it was unreasonable to expect the Palestinians to make an unconditional commitment to return to talks while the Israelis were continuing settlement building on Palestinian territory.
"Statehood for the Palestinians is not a gift to be given but a right to be acknowledged," he said.
"I warn the Foreign Secretary, if the United Kingdom abstains tomorrow it will not be a measure of our growing influence, it will be confirmation of our growing irrelevance to meaningful engagement in the search for peace. Abstention tomorrow would be an abdication of Britain's responsibilities."
His comments were echoed by former Liberal Democrat leader Sir Menzies Campbell who said: "Britain's failure to support the motion will cause profound damage to our reputation in the Middle East and flies in the face of public opinion at home and abroad. Recognition for the Palestinians is the right thing to do and something to which they are entitled."
Senior Tory backbencher Nicholas Soames acknowledged the "fiendish difficulties" of the situation in the Middle East, but added: "Whatever this resolution states these conditions are unnecessary and one sided and grossly unfair."
The calls came after France announced it is ready to support the resolution to upgrade the Palestinians' status at the UN from observer to non-member observer state, with other European states expected to follow suit. With the General Assembly dominated by countries sympathetic to the Palestinian cause - and no veto for members of the Security Council - the resolution looks set to be passed, despite the vehement opposition of both Israel and the United States.