Theresa May has dismissed the row over her chief negotiator saying she plans to threaten MPs with a “long” delay to Brexit as something “overheard in a bar”.

However, the prime minister again failed to rule out extending Article 50 – which Olly Robbins is alleged to have floated, if MPs still refuse to back her deal by the end of March.

The SNP said it showed Ms May’s claim she is ready to crash out of the EU if necessary had reached the “end of the road” because she had been “rumbled by your own loose-lipped Brexit adviser”.

Brexiteer Tories are furious after Mr Robbins was quoted as saying: “Extension [of Article 50] is possible but if they don't vote for the deal then the extension is a long one.”

Asked to “rule out” such a delay, the prime minister said: “I’m grateful that he has asked me that question, rather than relying on what someone said to someone else as overheard by someone else in a bar.

“The government position is the same. We triggered Article 50 – in fact this House voted to trigger Article 50.

“That has a two-year timeline that ends on the 29 March. We want to leave with a deal and that’s what we working for.”

Strikingly, the prime minister’s response did not deny that the choice before MPs is likely to be her deal or a long delay – rather than her deal, or a no-deal Brexit.

Top politicians' Brexit tweets haven't aged well Show all 18 1 /18 Top politicians' Brexit tweets haven't aged well Top politicians' Brexit tweets haven't aged well These billboards were plastered by campaign group Led By Donkeys @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well Undated handout photo issued by Led by Donkeys of their billboard featuring a blank tweet in Jeremy Corbyn's Islington North constituency in protest over what they claim is his lack of leadership on Brexit. PRESS ASSOCIATION Photo. Issue date: Tuesday February 12, 2019. For the past month, campaign group Led by Donkeys has been putting up posters all over the country featuring quotes mostly from hard-Brexit MPs which claimed the process of leaving the EU would be easy. The Labour leader is the group's latest target because of his failure to back a second referendum on Brexit. See PA story PROTEST Donkeys. Photo credit should read: Led by Donkeys /PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter

In his comments, overheard by an ITV News journalist, Mr Robbins contradicting the prime minister’s insistence that she will carry out a no-deal Brexit if necessary.

He was overheard saying: “The issue is whether Brussels is clear on the terms of extension. In the end they will probably just give us an extension.”

The negotiator also appeared to confirm that Ms May, as a cabinet minister hinted yesterday, plans to delay the critical decision until “the week beginning end of March”.

Steve Baker, the deputy leader of the hardline European Research Group of Tory MPs said Mr Robbins should be “appalled by this story”.

And Andrea Jenkyns, another Tory Brexiteer, tweeted: “If true, the PM should stop ignoring the wishes of the British people and disregarding her own red lines.”

In the Commons, Ms May also sought to calm Tory MP’s fears that she will compromise on leaving the EU customs union, in order to secure Labour votes and pass her stalled deal.