British Prime Minister Theresa May has faced calls to push for reform of Northern Ireland's abortion laws after the referendum, with scores of MPs prepared to act to rewrite the current legislation.

As the referendum on the Eighth Amendment looks set to be passed by a 2-to-1 majority, Northern Ireland will soon become the only part of Britain and Ireland where terminations are all but outlawed.

Liberal Democrat leader Vince Cable said Mrs May should take advantage of the current lack of a devolved administration and push for reform from Westminster.

Labour MP Stella Creasy said more than 140 parliamentarians had already signalled support for an effort to change the law in Northern Ireland.

Senior civil servants have been taking the majority of decisions within departments in Northern Ireland since the power-sharing administration at Stormont collapsed 16 months ago.

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Mr Cable said: "I believe in the principle of the right to choose, I think in the rest of the UK we have a sensible balance.

"The position in Northern Ireland is now highly anomalous and I think, probably, action will now have to be taken."

Asked if Mrs May should intervene, he said: "As long as you have devolved elected bodies then one has to respect their preferences, whether it's Scotland, Wales, Northern Ireland or London.

"Since there is, effectively, direct rule from Westminster, the government has responsibility and it can and should take the opportunity to deal with this issue properly."

Ms Creasy, who led a campaign to allow Northern Irish women to access NHS terminations for free in England, said "21st century abortion laws" should be extended across Britain.

She said if 2.5 million Irish women had won the right to choose "we can't leave behind one million women in Northern Ireland".

"The UK parliament needs to act to make sure every citizen has access to 21st century abortion laws and we will be tabling amendments - in partnership with Northern Irish campaigners - to help make that happen," she said.

DUP MP Ian Paisley Jr said Northern Ireland would "not be bullied" into accepting abortion.

The forthcoming Domestic Abuse Bill promised by ministers could be used as a vehicle for MPs hoping to change the law in Northern Ireland.

Abortions are currently only legal in Northern Ireland if the life or mental health of the mother is at risk.

While political leaders in the south were at the forefront of efforts to liberalise the law during the referendum campaign, a majority of politicians in Northern Ireland do not favour the radical law change.