Theresa May’s chances of delivering Brexit on 29 March are fading fast after senior ministers privately admitted more time is needed even if her deal wins the backing of parliament.

Senior Tories have accepted that the sheer amount of legislation parliament must pass to prepare for Brexit regardless of whether Ms May’s plans are approved, makes a withdrawal on the agreed date almost impossible.

One cabinet minister told The Independent that in the unlikely event the prime minister’s deal is actually approved on Tuesday, then a couple more weeks would still be needed – if as expected it is not, then a longer delay of Brexit looks inevitable if a no-deal scenario is to be avoided.

Despite the admission from within the cabinet, Downing Street attempted to play down the chances of any extension to the Article 50 negotiating period on Friday by saying that it is not “government policy”.

Ms May looks set for a historic defeat when she puts her deal to the House of Commons on Tuesday, with some estimates suggesting she will lose by more than 200 votes.

The delay in determining the country’s path would also push back the ability of parliament to pass around six essential pieces of legislation, making a 29 March exit unlikely despite Number 10’s claims.

But the inevitability of a delay to Brexit was highlighted by one cabinet minister who told The Independent that a short extension of Article 50 would probably be required to implement a deal that is approved.

The frontbencher said: “It will be difficult to pass the legislation by the end of March, even if the deal goes through.

"Brexit betrayal" march in London Show all 43 1 /43 "Brexit betrayal" march in London "Brexit betrayal" march in London A protester holds an anti-BBC sign Angela Christofilou/The Independent "Brexit betrayal" march in London A pro-brexit demonstrator holds a sign in the picket line Angela Christofilou/The Independent "Brexit betrayal" march in London A protester carrying a noose at the "Brexit betrayal" march. The man carrying it told a reporter: "That's what the traitor May deserves." 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“But no one is going to object if we need a couple more weeks.”

They argued that both the EU and Brexiteers were unlikely to object to a short delay as long as the UK’s withdrawal was absolutely guaranteed.

The government must pass a series of bills including those relating to trade, immigration and agriculture to ensure the country has the legislative framework in place come Brexit day.

Until now Downing Street has been adamant that it would be possible to get all the new laws passed, even if it meant cancelling a commons break for half-term in February and having MPs sit at the weekends. As late as Friday morning the prime minister’s official spokesman told reporters any delay to Brexit is not government policy.

But the admission that more time will be needed even if the PM wins the vote, let alone if she loses as expected, means Brexit could be knocked back deep into 2019.

MPs have power to stop no-deal Brexit, says Jeremy Hunt

Earlier on Friday, a senior minister told the Evening Standard: “The legislative timetable is now very very tight indeed.

“Certainly, if there was defeat on Tuesday and it took some time before it got resolved, it’s hard to see how we can get all the legislation through by 29 March.”

Mr Hunt appeared to pull the rug from under Ms May’s warning’s that MPs voting against her deal were pushing the country closer to a no-deal Brexit, when he said it was “highly unlikely” that MPs would not find a way to thwart a disorderly exit if they wanted to.

In a dramatic intervention, the foreign secretary also warned that voting down Ms May’s deal next week could actually prevent Brexit, saying it would bring in “Brexit paralysis” with the “possibility in sight” of the UK remaining in the EU.

Amber Rudd refuses to rule out resigning if government pursues a no-deal Brexit

Speaking about no deal, Mr Hunt said: “We’ve seen from this week that parliament has the ability to assert itself and to shape outcomes. I think after this week the idea that parliament is going to do nothing at all is highly unlikely.”

He said thwarting Brexit would be “potentially very damaging” and warned that it was now a choice between Ms May’s deal and no Brexit. This marks a shift in tone, as the prime minister has repeatedly set out a choice between her deal and no deal.

Government insiders are expecting some kind of extra help for Ms May from the European Union by Monday, which they hope will allay some of the concerns that her critics have about the “Irish backstop”. But it is unlikely to be a legally binding guarantee that the UK can exit from it unilaterally, which is what many Tories and Ms May’s DUP partners in government want.

Either way one BBC analysis estimates the government is heading for defeat on Ms May’s withdrawal blueprint by a crushing margin of 228 votes next week.