MPs should be “brave” and not allow the far right to “dictate” policy over Brexit, London Mayor Sadiq Khan has said. 

The Labour politician was responding to claims by Transport Secretary Chris Grayling that a failure to leave the EU on March 29 would see “the emergence of forces like that”.

It comes amid heightened speculation that if Theresa May’s Brexit deal is rejected, Article 50 could be extended and ministers could be forced to back a second referendum.  

Khan, a high-profile supporter of a so-called People’s Vote, told Radio Five Live’s Pienaar’s Politics: ″I’m hoping the British public do take back control and that this campaign is a more positive one.

“The idea that we should allow a fare of the far-right to dictate our policy I find astonishing. 

“The far-right, for example, wouldn’t want someone who looks like me to be the Mayor of London. Does that mean I don’t stand to be mayor of London?

“The far-right don’t want many, many things. The idea that this government are capitulating to the far-right as a reason for not holding a public vote I find astonishing.” 

It comes after a number of pro-Brexit protests outside Westminster have been hijacked by far right groups. 

Tory remainer Anna Soubry faced chants of “Nazi” and “traitor” as she was mobbed outside Westminster by one group of protesters over her support for a second referendum. 

One protestor who took part in a march led by English Defence League (EDL) founder Stephen Yaxley-Lennon, also known as Tommy Robinson, even brought his own gallows to a Parliament Square rally in December.   

Labour MP Jim Fitzpatrick told the Commons last week he was “not far off” backing Theresa May’s Brexit deal in the critical vote on Tuesday. 

Among other reasons, the former minister said people being subjected to abuse outside parliament demonstrated “just how toxic this issue is and it has to end”. 

Jeremy Corbyn also appeared to dash hopes that Labour would back a re-run of the Brexit vote on Sunday when he told the BBC Andrew Marr Show that he wanted May’s deal to be renegotiated. 

But Khan called for MPs to be “brave” and said a second vote would be “cathartic”. 

He also claimed MPs were being presented with a “false narrative” the only choice was between May’s deal and no-deal. 

“The PM is brazenly blackmailing MPs to support a bad deal,” Khan claimed.

“And actually, by the way, the best way to heal divisions and to deal with issues of discord isn’t to bury them away, which is what a ‘bad deal or no-deal’ would do, but I actually think a public vote would be cathartic, but also a proper campaign now we know the mistruths, now we know the tricks used by the Brexit campaign [they] would be addressed in a new public vote.” 

Grayling, who is calling for MPs to back May’s deal, said the UK risks ushering in “extreme” political forces, and that there was evidence of this on the continent.

“We have seen in pretty much every other country in Europe the emergence of new significant political parties at the political extremes, and my concern is if we say to those 17.4m people who voted to leave ‘actually, guys, we are not leaving after all’, we will see the emergence of a force like that and we will see real impact on our politics.” 

Khan was also challenged over whether he thought London was unable to succeed should Britain drop out without a deal.

He said London would recover from any economic dip, and added: ″My point is that we would be more successful as part of a reformed EU. My concern is that if a false narrative is given of ‘accept this bad Brexit deal or there is no alternative whatsoever’ that is blackmailing MPs to vote a certain way. I think MPs should be brave and vote to reject the deal on Tuesday. 

“And if we can’t get a general election the next best thing is for the public to take control bearing in mind there is gridlock in parliament.”