Theresa May’s government has been accused of failing to restrain the furious backlash against this week’s high court judgment about article 50, as one of her own MPs resigned, increasing the political pressure as she pledges to stick to her Brexit timetable.

Stephen Phillips, the MP for Sleaford and North Hykeham in Lincolnshire, stepped down on Friday with immediate effect. He said he was unhappy that the government had not planned to consult parliament before triggering article 50 – the issue that led to Thursday’s ruling.

Former ministers warned that the febrile tone of media coverage, which included the judges who ruled against the government being condemned as “enemies of the people” by the Daily Mail, risked poisoning public debate.

Dominic Grieve, the Conservative former attorney general, said reading hostile coverage in the Mail and the Daily Telegraph “started to make one think that one was living in Robert Mugabe’s Zimbabwe … I think there’s a danger of a sort of mob psyche developing – and mature democracies should take sensible steps to avoid that”.

Labour also raised concerns about the absence of a ministerial response to the media coverage. Charles Falconer, who was lord chancellor under Labour between 2003 and 2007, said faith in the “independence and quality” of the judiciary was being undermined “by this Brexit-inspired media vitriol”, in an article written for the Guardian.

On Saturday, Jeremy Corbyn will accuse the government of opposing democratic scrutiny because “frankly, there aren’t any plans, beyond the hollow rhetoric of ‘Brexit means Brexit’”.

The Labour leader will say in a speech: “Thursday’s high court decision underlines the necessity that the prime minister brings the government’s negotiating terms for Brexit to parliament without delay.

“Labour accepts and respects the decision of the British people to leave the European Union. But there must be transparency and accountability to parliament about the government’s plans.”

May telephoned European leaders to tell them again that she would meet her self-imposed deadline and trigger article 50 by the end of March 2017, despite losing the high court case. The prime minister has otherwise not entered the row.

Her spokesman refused to condemn the media coverage on Friday, saying: “I don’t think the British judiciary is being undermined.” But the pro-remain former business minister Anna Soubry told the Guardian: “I think we have to call this out and say ‘not in my name’.”

Soubry, a Tory MP and former journalist, said the tone of some reports since the referendum result was “inciting hatred … It needs somebody like Boris Johnson to step up and speak out. He’s our foreign secretary and he knows what the reaction of the rest of the world is as they look at our great country and are horrified. What message are we sending out to the rest of the world? Probably that this nation is in grave danger of losing the plot – and I think we might have done.”

Johnson, who was in Berlin on Friday, used a press conference to play down the significance of Thursday’s ruling, which the government says it is “confident” it can overturn on appeal at the supreme court next month. The high court ruled that it was not constitutional for the government to trigger article 50 without a vote by MPs.

Johnson urged his German counterpart, Frank-Walter Steinmeier, not to “read too much into the legal decision that you have just seen or indeed the Sturm und Drang, if that’s the word I want, that is going on in parliament at the moment. The direction is very clear, the will of the British people was expressed very clearly and it is the decision of Theresa May and her government to get on and make that process work.”

In his resignation letter to George Clark, the chairman of the Sleaford and North Hykeham Conservative Association, Phillips said he could no longer live with being labelled a Conservative.

As well as his unhappiness over the Brexit process, he also attacked the government for “shirking” its responsibility for unaccompanied child refugees and changes to the way international aid was spent. Phillips said: “Some will label me a quitter or, no doubt, worse. Those are labels with which I can live. The label Conservative no longer is.”

The Conservatives are highly likely to retain Phillips’ seat, which he held with a majority of 24,000; but his departure creates another distracting byelection, after David Cameron left his Witney seat and Zac Goldsmith stepped down to fight Richmond Park as an anti-Heathrow expansion independent.

On the other side, prominent Brexit supporters have told the Guardian they believe MPs and peers are gearing up for an audacious bid to keep Britain in the EU “via the backdoor”, underlining the vicious parliamentary battle that may lie ahead if the government loses its appeal against the article 50 verdict.



A Tory MP, Dominic Raab, accused colleagues of trying to “steal the referendum, not deliver on it”. Meanwhile, Labour’s Gisela Stuart, who chaired the Vote Leave campaign, said those in her party and others who were demanding that the UK remain inside the single market were effectively trying to scupper the will of the people.

Raab, the former justice minister who now sits on parliament’s select committee on leaving the EU, said: “As Lib Dem and Labour peers and MPs are now making clear, the ruling will be exploited by those in denial of the referendum verdict, who want to see us stay in the EU via the backdoor. Bluntly, they want to steal the referendum, not deliver on it.”

Stuart, who chaired the campaign to take Britain out of the EU, said the courts were entitled to rule on their interpretation of the process. “But I think it is incumbent on parliamentarians to then also recognise that they don’t have sovereignty over the people. The people have made it quite clear they want to leave,” said the MP who now leads Change Britain, a group that includes prominent Brexiters such as Michael Gove.

In an interview for Radio 4’s Week in Westminster to be broadcast on Saturday, Stuart warned against MPs using debates about the single market or customs union “in pursuit of negating the people’s will”. Asked if she thought any politician calling for Britain to remain in those organisations was trying to scupper the Brexit vote, she replied: “Yes, I think I do, because what people made quite clear during that referendum is that democratic accountability for them was far more important than anything else.”

The former Cabinet minister John Whittingdale agreed, arguing that the referendum result meant that even if the supreme court upholds the decision then parliament should either overturn it or every MP should vote in favour of triggering article 50. “I don’t want there to be any conditions on the outcome of the negotiations,” he said, adding that even if European countries block economic access, Britain must still leave the EU.



Lord Kerslake, former head of the civil service. Photograph: Steve Parsons/PA

Bob Kerslake, the former head of the civil service, said the government had been caught out trying to avoid a difficult debate in parliament. “The government would be much better off thinking how to tackle the issue,” he said.



The peer, who has been active in his scrutiny of legislation since joining the House of Lords, said the British public voted to leave the EU but that left many unanswered questions. “Whatever else it changed, I don’t think the referendum changed the fact of parliamentary democracy or that we operate under the rule of law.”



Meanwhile, the legal and political complications facing May intensified on Friday after the Welsh government’s counsel general, Mick Antoniw, said it would formally join the complainants’ side in the supreme court case next month.



Scottish government sources said Antoniw’s intervention increased the chances that Nicola Sturgeon would also join the action. Both devolved governments are concerned that their legal and parliamentary interests are being overlooked in May’s rush to push through article 50 without a vote.

The move would force the UK government to explain why it believed leaving the EU was only a matter for Westminster, even though it would have a direct effect on the powers of all three devolved parliaments in Edinburgh, Cardiff and Belfast. Scottish government lawyers have already been sitting in on the case as observers.

In his statement on Friday, Antoniw said: “Having considered the judgments in both matters, I consider that they raise issues of profound importance not only in relation to the concept of parliamentary sovereignty but also in relation to the wider constitutional arrangements of the United Kingdom and the legal framework for devolution.”