Foreign Secretary William Hague is under pressure to back a historic vote at the United Nations granting recognition of a Palestinian state.
But in a Commons statement, Mr Hague said Britain would only support the resolution at tonight's meeting at the UN General Assembly in New York if the Palestinians gave a commitment to an unconditional return to the negotiating table with Israel.
He said the UK would also require an assurance the Palestinians would not seek to extend the jurisdiction of the International Criminal Court (ICC) over the Occupied Territories.
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Mr Hague said: "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."
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 said it was unreasonable to expect Palestinians to make an unconditional commitment to return to talks while the Israelis were continuing settlement building on Palestinian territory.
Mr Alexander added: "Statehood for the Palestinians is not a gift to be given but a right to be acknowledged.
"If the UK 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. "
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 added: "Whatever this resolution states these conditions are unnecessary and one-sided and grossly unfair."
The calls came after France said it was ready to support the resolution to upgrade the Palestinians' UN status to non-member observer state – the status also held by the Vatican – 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.
The Israelis have already said they will not return to negotiations following the vote, arguing it would undermine efforts to secure a peace settlement.
Mr Hague told MPs he had appealed to Palestinian president Mahmoud Abbas – who he praised as a "courageous man of peace" – not to move the resolution, but to give US President Barack Obama the chance to launch a fresh peace initiative.
He said: "We pointed out a UN resolution would be depicted by some as a move away from bilateral negotiations with Israel."
Mr Hague said a public commitment by the Palestinians that they were ready to resume negotiations with Israel without pre-conditions was "indispensable" if the UK was to vote in favour.
The Palestinians also needed to make clear they would not seek to build on the resolution to pursue ICC jurisdiction over the Occupied Territories as this could make a return to negotiations "impossible", he said.