BORIS Johnson has suffered a fresh wave of setbacks on Brexit, as EU leaders shredded his suggested alternative to the Irish backstop and centrist Tory MPs revolted against Downing Street’s plan to campaign for no-deal in the impending general election.

Scotland’s highest court also warned it stood ready to correct any “demonstrable unlawfulness” if the prime minister tried to disobey the law on delaying Brexit in the absence of a deal.

Mr Johnson now faces a showdown with Parliament on October 19 which will determine if he can deliver his “do or die” promise to take the UK out of the EU on Hallowe’en.

Read more: Court delays decision on forcing Boris Johnson to seek Brexit extension

The first Saturday sitting in the Commons since the Falklands crisis of 1982 is expected to coincide with thousands of protestors at Westminster demanding a new EU referendum.

Just one week after the PM presented his proposal for a revised Brexit deal to Brussels, it was torn apart by Michel Barnier in the European Parliament.

The EU’s chief negotiator was updating MEPs on the progress of talks ahead of next week’s EU Council, seen as the last, slim chance for Mr Johnson to secure a new Brexit deal.

Mr Barnier said there could yet be a deal with goodwill on both sides but said the UK plan relied on untested technology for customs checks in Ireland. He said: “We are not really in a position where we are able to find an agreement.

“The proposal of the British Government as things stand isn’t something we can accept. It replaces an operational, practical, legal solution [with] one that is simply a temporary solution.”

Read more: Brown warns no-deal could make UK a ‘paradise for spivs’

Mr Johnson’s alternative to the backstop would see Northern Ireland aligned with EU single market rules, but removed from the EU customs union. His plan also gives the pro-Brexit DUP a veto over the single market element.

Mr Barnier said the customs proposals, with checks away from the border at businesses or done electronically, had not been tested and relied on technology which “has yet to be developed”. He said: “We need operational real controls, credible controls, we are talking about the credibility of the single market here – its credulity to consumers, to companies, and to third countries that we have agreements with.”

He said the EU needed workable solutions “today not tomorrow”.

Brexit Secretary Stephen Barclay will meet Mr Barnier in Brussels today. Mr Johnson, who says he remains optimistic about a deal, is due to meet Taoiseach Leo Varadkar today in a lastditch attempt to win over Dublin. However the Irish PM told the Dail yesterday the UK’s customs plan presented a “grave difficulty”.

Read more: Map shows how Brexit affects all of Scotland

There was also criticism from EU figures of Number 10’s spin operation. On Tuesday, Number 10 sources briefed that a deal appeared “essentially impossible” after Mr Johnson and German Chancellor Angela Merkel had a row in a phone call. It prompted EU Council President Donald Tusk to accuse Mr Johnson of trying to win “a stupid blame game”.

European Commission President JeanClaude Juncker told MEPs: “We are not accepting this blame game which started in London. We are not to be blamed but we will see in the next coming days how things will develop.”

Guy Verhofstadt, the parliament’s Brexit negotiator, was more scathing. He said: “It is a blame game. A blame game against everybody. A blame game against the [European] union, against Ireland, against Mrs Merkel, against the British judicial system, against Labour, against Lib Dems, even Mrs May.

“The only one who is not to be blamed is Mr Johnson apparently. All those who are not playing his game are traitors, are collaborators, are surrenderers.

“The real traitor is he or she who risks bringing bringing disaster on his country, its economy and its citizens by pushing Britain out of the European Union. That in my opinion is a traitor.”

However Brexit Party leader Nigel Farage told the assembly that Brussels had stopped negotiating in “good faith” and was insulting the UK. “You are not looking for solutions. You are looking to put obstacles in our way.”

Read more: Brown warns no-deal could make UK a ‘paradise for spivs’

Mr Johnson also faced trouble at home, as the 100-strong One Nation group of centrist Tory MPs warned him not to make no-deal the party’s policy in the general election. It followed a briefing to the Spectator – widely attributed to the PM’s chief adviser Dominic Cummings – which said: “If this deal dies in the next few days, then it won’t be revived. To marginalise the Brexit Party, we will have to fight the election on the basis of ‘no more delays, get Brexit done immediately’.”

The One Nation group’s leader, Damian Green, said he had looked Mr Johnson in the eye and been reassured he had “no intention” of putting a no-deal policy in the next manifesto.

“I accept and believe the reassurances,” he said, although others were more sceptical. Between 50 and 80 Tory MPs have indicated they are not prepared to stand on a no-deal platform.

If the PM fails to get a deal next week, the Benn Act requires him to seek an extension of at least three months. The PM says he would rather “die in a ditch”, but has also promised to obey the law. The October 19 sitting of the Commons will therefore be the moment he must establish exactly how he will solve this apparent contradiction.

There are reports he might also try to force MPs to vote on whether to revoke Brexit, or even invite a no confidence vote in an attempt to force an election. However MPs could seize control of the order paper to frustrate him.

Read more: Court delays decision on forcing Boris Johnson to seek Brexit extension

he Court of Session in Edinburgh delayed ruling on a legal attempt to enforce the Benn Act until October 21 to see how the politics “played out”.

At Holyrood, SNP Brexit Secretary Mike Russell told MSPs: “I think there is a general view that whatever is taking place in 10 Downing Street, it is so outside the norms for the Prime Minister, or indeed for any civilised government, that we do wonder what will come next. “The damage it is doing is immense.”

Jeremy Corbyn said Labour MPs would “do everything we can in Parliament, including legislating if necessary” to ensure the PM asked for the three-month Brexit extension.