British MPs will vote on Prime Minister Theresa May's EU withdrawal deal on January 15, the government said Tuesday, while denying growing speculation it might seek to delay Brexit if the agreement is rejected.

May postponed an initial vote last month in the face of opposition from all sides of the House of Commons, but has now set it for next Tuesday evening after 1900 GMT, following five days of debate which start on Wednesday.

May is still struggling to convince both opposition lawmakers and her own Conservative party to back the divorce agreement, heightening fears Britain could leave the European Union on March 29 without a deal.

She has promised to secure further assurances from the EU on the most controversial elements of the Brexit deal relating to Northern Ireland, and has held talks with European leaders in recent days.

"The work to secure those assurances is ongoing," her spokesman said, adding that the prime minister hoped to have something to offer MPs before next week's vote.

May is hosting several drinks parties for lawmakers this week in a bid to win them round, arguing her deal is the best compromise that ends EU membership while protecting jobs.

Environment Secretary Michael Gove told cabinet colleagues that critics holding out for a better deal were like swingers in their mid-50s waiting for Hollywood star Scarlett Johansson to turn up on a date.

But with opposition among MPs still strong, there is growing speculation London could seek to delay the EU's two-year Article 50 exit process to allow more time to get the deal through parliament.

An EU diplomatic source told AFP that "we are convinced that Theresa May will request a postponement if the agreement is rejected in the British parliament."

But May's spokesman insisted: "We will not be extending Article 50.

"There are people in the European Union who are discussing this issue, but that is not the position of the UK government."

'Very hypothetical'

The other 27 EU leaders have repeatedly said they will not reopen the deal struck with Britain in November, which covers key separation issues such as money and expatriate citizens' rights.

But they issued a joint statement at an EU summit last month emphasising the temporary nature of the so-called backstop arrangement designed to keep open the UK border with Ireland after Brexit.

And Irish Prime Minister Leo Varadkar told the Irish Times there were discussions on whether the EU could offer "a further set of written guarantees, explanations and assurances".

The backstop would keep open the border between British Northern Ireland and EU member Ireland after Brexit by temporarily aligning Britain with EU trade rules.

Eurosceptic Conservatives and Northern Ireland's tiny Democratic Unionist Party (DUP), which props up May's government, fear it could tie London to Brussels for years to come.

However, France's Europe Minister Nathalie Loiseau said "there is nothing more that we can do" -- and warned against putting too much faith in talk of extending Article 50.

"I don't work on hypotheses -- the current situation is complex enough... Let's stick to where we are now," she said.

An EU diplomat also told AFP that the idea of delaying Brexit "is a very hypothetical option".

Any extension to Britain's departure would be complicated by the elections to the European Parliament in May. After Brexit, it will no longer be represented in the assembly.

No deal plans

May is looking at a possible time limit to the backstop arrangement and increased parliamentary scrutiny to try to sway MPs.

But if her efforts fail, many fear Britain could leave the EU with no deal, with potentially disastrous legal and economic consequences.

A cross-party group of MPs on Tuesday voted to amend a finance law to limit the government's tax-raising powers in the event of "no deal" in an attempt to avert such a scenario.

Downing Street said earlier that the amendment, while "not desirable," was an "inconvenience rather than anything more significant".

The impact of a disorderly Brexit would also be felt across Europe, including in the EU budget.

May's deal sets out plans for a post-Brexit transition period in which Britain would keep making financial contributions until December 2020.

EU budget commissioner Gunther Oettinger said that without this, "we would be short a figure in the billions of euros for the rest of the year and a higher figure for 2020".

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