By Rosa Prince and Martin Beckford
Pro-choice Labour MPs had been planning to back an amendment to the Embryology Bill that would allow terminations in Northern Ireland, the only part of Britain where the procedure remains illegal.
They have changed their minds after being privately warned by ministers that with the Stormont executive close to collapse, the move could tip the province's politicians into withdrawing from negotiations.
The MPs still plan to push ahead with separate plans to make access to abortion easier in the rest of the country by removing the requirement for two doctors' signatures and allowing nurses to carry out early-stage terminations, however.
But they face determined opposition from pro-life MPs, backed by church groups, when the Bill is debated in the Commons on Wednesday.
Mark Pritchard, Conservative MP for The Wrekin, said the decision not to legalise abortion in Northern Ireland was a ``welcome U-turn'' but added: ``The decision appears to be more about extending the political life of the Prime Minister - rather than the Government extending the lives of the unborn.
``It appears ministers are still determined to introduce 'drive-thru' abortions where mothers can bypass the advice of their local GP, drive straight to their local clinic and place an order for an abortion.''
The Human Fertilisation and Embryology Bill, which also includes measures allowing human-animal hybrid embryo research and the creation of ``saviour siblings'', has already been the cause of some of the most heated exchanges in Parliament in recent years.
A series of amendments to lower the upper time limit for abortions from 24 weeks was defeated after an impassioned debate in May and the Bill had been due to clear the Commons in July.
But it was suddenly halted on the intervention of Harriet Harman, the Leader of the House, who was said to be keen to see the Northern Ireland amendment pass and wanted more time to raise support for it.
Pro-choice MPs had been confident of success when the Bill returns to the Commons next week, particularly given the forthcoming departure from the Cabinet of Ruth Kelly, the Transport Secretary, who as a committed Catholic had forced Gordon Brown to allow ministers a free vote when it was last debated.
But the Ulster political situation has deteriorated recently, with the Executive failing to meet as scheduled as a result of a disagreement between unionists and republicans over the devolution of policing and justice.
While abortion is one area where Northern Ireland's politicians largely concur - with both Sinn Fein and the Democratic Unionist Party opposed to legalisation - ministers fear that forcing the amendment through could undermine their attempts to broker an agreement.
As a result, pro-choice Labour MPs have been taken aside and warned not to proceed with their plan.
An amendment has been tabled by Diane Abbott, Labour MP for Hackney north, for but without the full backing of the powerful female Labour pro-choice group, it has little chance of success.
The message was underlined at the ``Ulster Fry'' breakfast meeting at Labour Party Conference, where MPs mingled with Northern Irish politicians - who told them they would consider breaking off communication with the Government over the issue.
Around 1,400 girls and women travel from the province each year to have a termination on the mainland, as the 1967 Act which legalised abortion in the rest of the country was never extended to Northern Ireland.
The Fpa, formerly the Family Planning Association, has now launched an online video campaign aimed at MPs urging them to end the ``discrimination'' that pregnant women in Northern Ireland face if they do not want to have their baby.
Julie Bentley, chief executive of the Fpa, said: ``The leaders of the four main political parties and the leaders of the main church groups in Northern Ireland have all demanded that abortion should remain highly restricted but only 16.6 percent of the Northern Ireland Assembly are women.
``So the situation exists that groups of men are making decisions about women's lives and creating a division of rights and entitlement between women, on the basis that they live in different regions of the UK.''