THERESA May told her MPs to vote against the Common Market 2.0 in last night’s indicative votes, because of fears it could weaken the case against Scottish independence, a BBC journalist has claimed.

Newsnight reporter Nicholas Watt says the Tory leader believed the proposal put forward by her former minister Nick Boles “would have destroyed the main pro-UK argument in a Scottish independence referendum”.

The Common Market 2.0, or Norway Plus plan, tabled by Boles and backed by MPs from all parties, would commit the Government to joining the European Free Trade Association (EFTA) and European Economic Area (EEA). It would mean the UK remaining part of the EU single market, which in turn would mean freedom of movement.

It was defeated by 282 votes to 261, despite being supported by Labour and the SNP.

In a series of tweets, Watt said May had “ordered a particularly aggressive whipping operation against” the Common Market 2.0 plan.

The reporter claimed the Prime Minister believed it “could threaten integrity of UK”.

He said: “PM feared that if UK stayed in single market through EFTA pillar of EEA that could increase support for Scottish independence.

“SNP would argue in an independence referendum: vote Yes to be fully in EU while maintaining full access to UK market because UK would be in single market.

“PM believes that at a stroke the Boles plan would have destroyed main pro-UK argument in a Scottish independence referendum: stay in UK as the only way to maintain full access to Scotland’s largest market in rest of UK.”

The SNP claimed the Prime Minister was “preparing to trash the UK economy, and all for a line on a pro-Union leaflet”.

They added: “Theresa May is deliberately damaging the UK ... in order to blackmail Scotland into staying in it and going down with the ship.”

Pete Wishart claimed the Tories were willing to “make the UK poorer and more isolated to stick one to the SNP.”

“Where we have been reasonable and conciliatory she has been gaming against independence,” he added.

Deidre Brock called it disgraceful. She tweeted: “So May heavily whips against the softer Brexit option tonight in part because she wants to keep trade threats dangling over the people of Scotland for next #Indyref – thought I was beyond being shocked by this place but no! disgraceful”.

A spokesman for the Scottish Tories said: “The Prime Minister has always made keeping the Union together a priority.

“It’s no surprise to see SNP MPs – who want to destroy that same Union – disagree with her.”

Shortly after the motion’s defeat in the Commons on Monday, Boles resigned from the Tories, accusing May of being unable to compromise.

On Twitter Boles made clear that he would not be joining the new party, Change UK, formerly The Independent Group. “I am resigning the Conservative whip with immediate effect. The Conservative Party has shown itself to be incapable of compromise so I will sit as an Independent Progressive Conservative,” he said.

In a sign of the splits within the party, Mark Francois, a Brexiteer Tory MP told the BBC he believed the Chancellor had been privately encouraging MPs to support a customs union.

“This evening ... an attempted coup in the House of Commons by MPs against the people was defeated.

“A number of members of the Cabinet led by Philip Hammond, utterly in cahoots with backbenchers across the house, attempted to stop us leaving the European Union.

“If you’re listening Mr Hammond, my fraternal message to you is: ‘Up yours’,” he said.

Damian Hinds, the Education Secretary, paid tribute to his former colleagues. He told BBC Radio 4’s Today programme “Nick’s a great colleague and a great person and I’m sorry he felt he had to do what he did”, but insisted the Government’s deal was a good compromise. “Time is very short, and the default position is that we leave in 10 days’ time without a deal,” he said.