The 40-odd Brexiteers who drive the Conservative Party car believe in Brexit at all costs. They revolve around the European Research Group (ERG), headed by that favourite of the Tory rank and file, Jacob Rees-Mogg.

He follows in the footsteps of former ERG chairs Suella Fernandes and Steve Baker, both now Brexit ministers in the Department for Exiting the EU. Fernandes famously claimed last year that there would not be a Brexit divorce bill of billions of pounds, labelling such claims “Project Fear”, when in fact it will be up to £39bn; Baker was forced last week to make a statement in the House of Commons apologising for wrongly calling into question the political impartiality of the civil service.

Hard Brexit cheerleaders in the Cabinet include Boris Johnson and, of course, Michael Gove, as well as Andrea Leadsom, Penny Mordaunt, Chris Grayling and Liam Fox. They, along with their allies in the media and beyond, are driven by nationalism and, more often than not, a libertarian belief in unfettered free markets. Part of the reason Ukip wallows in the polls is because these Tory Brextremists have stolen many of their clothes – but they are all part of the same club.

Unlike Baker, Rees-Mogg has refused to apologise for impugning the civil service, instead doubling down on assertions that it is politically influenced, alleging that Treasury civil servants are fiddling the figures to show Brexit in a less than favourable light. This prompted the former Treasury permanent secretary, Lord Turnbull, yesterday to accuse them of adopting dangerous tactics similar to those of right-wing German nationalists between the two world wars.

Turnbull told The Observer: “After the First World War there was an armistice, but the German army were then treated as the losers. Then, at the start of the Nazi era, the ‘stab-in-the-back’ theme developed.

“It argued that ‘our great army was never defeated, but it was stabbed in the back by the civilians, liberals, communists, socialists and Jews’. This is what I think these critics are trying to do. They are losing the argument in the sense that they are unable to make their extravagant promises stack up, and so they turn and say: ‘Things would be OK if the civil service weren’t obstructing us’.”

But the attack on the institutions that maintain our democracy by these Brextremists goes far beyond the civil service. It started in November 2016 with the judiciary, which is an important check and balance on the abuse of power by those in government: it ultimately upholds the rule of law in this country.

Gina Miller, a private citizen, brought a High Court case asserting the right of Parliament – as opposed to the Prime Minister – to instigate the process of our withdrawal from the EU. Miller won the case and was consequently attacked online for being foreign-born, and was subject to racial abuse and threats of sexual violence by those purporting to be Brexit supporters simply for exercising her rights as a British citizen.

Ironically, Miller had in fact sought to uphold parliamentary sovereignty, supposedly the raison d’être for the Leave vote. The judges who handed down the ruling in her case – one that was upheld by the Supreme Court in January 2017 – were called “enemies of the people” on the front page of the Daily Mail, with the Mail Online referencing the sexuality of one of the judges and their backgrounds. The author of the ugly front-page piece was James Slack, who Theresa May appointed as her press spokesperson in February 2017.

The other important check on the power of the executive in the British constitution is, of course, Parliament. Every step of the way through the Brexit process, the Conservative Government has sought to withhold information on Brexit from the House of Commons. Just last week, Buzzfeed published leaked details of a cross-department briefing paper on the economic impact of Brexit which showed that all the alternative models to staying in the EU will severely damage the economy.

The Government did not oppose the motion tabled by Labour last Wednesday forcing them to agree to publish the paper. This is because they knew they wouldn’t have a majority if it were put to a vote, given the substantial number of Tory rebels there would be.

In December, a number of brave Tory MPs defied the Government whip to insist Parliament be given a meaningful vote on whatever deal Theresa May comes back from Brussels with at the end of this year. Beforehand they were accused in and out of Parliament by Conservative colleagues of trying to thwart Brexit, claims that were followed up by The Daily Telegraph, which plastered their pictures on a front page, labelling them “mutineers”. This led to Anna Soubry, my fellow co-chair of the All-Party Parliamentary Group on EU Relations, receiving no less than 13 death threats, which she reported to the police.

Then there is this country’s independent central bank, the Bank of England, which is guardian of the money supply and helps maintain financial stability. In the aftermath of the June 2016 referendum, the pound plummeted in the financial markets. The least the Brextremists could do was apologise for the ensuing mess. But instead they turned their fire on and called for the head of the one person who deserves credit for steadying the ship: the governor of the Bank of England, Mark Carney.

Carney and his colleagues, as well as cutting base rates to 0.25 per cent, announced purchases of Government bonds, corporate bonds and a scheme to provide cheap funding to banks to ensure that the cut in that rate was passed on to the interest rates paid by people and firms. These measures were instrumental in steadying the ship but, because he has been unafraid of spelling out the economic consequences of Brexit – which he calculates has already cost the UK £200m per week in lost growth – he has come under sustained attack from the ERG, with Rees-Mogg calling him “an enemy of Brexit”.

Then there are the darker and more sinister claims by Brextremists of what will follow if Brexit is not delivered to their satisfaction. As I said in the House of Commons back in December, following the death threats made to Anna Soubry and others: “What they do is to imply to varying degrees that if Brexit … is not delivered in certain terms, there will be violence. For example, the leading Ukip MEP Nigel Farage said at a dinner earlier this year that if Brexit was not delivered to his satisfaction he would be ‘forced to don khaki’ and to ‘pick up a rifle’.”

In short, the actions of these Brextremists risk taking our country into a very dark place indeed. Lord Turnbull is right: it has a strong whiff of the 1930s about it. As patriots, we all have to call it out and defend our right to challenge the Government. We must argue for a different future for our country. This brings me to the Labour Party.

I have consistently called for the Labour front bench to adopt a clearer position against this extremism and the unfolding Tory Brexit catastrophe by, at the very least, committing to ensure the UK continues to participate in the EU single market – which protects workers, consumers and the environment – and the customs union if Brexit happens.

The strongest advocates of doing these two things are actually trade unionists. As TUC general secretary Frances O’Grady said earlier this month, “While we know that the single market and the customs union aren’t perfect, the TUC’s analysis clearly shows that they are far better for workers’ jobs and rights than any other trade models.”

The overwhelming majority of our membership – who voted for Jeremy Corbyn in the 2015 and 2016 Labour leadership elections – also support staying in both entities. Just last week, the former Greek finance minister, Yanis Varoufakis – who famously fell out with the EU – came to Parliament at my invitation to make the Marxist case for the Labour Party to adopt a “Norway-plus” model as policy (ie staying in the single market).

In truth, one of the biggest obstacles to the leadership adopting a less ambiguous position that would put clear red water between us and the Tories on Brexit is that so many people believe I – and other Labour MPs – make our Brexit arguments out of a desire to oppose the Labour leader.

I did not support Jeremy Corbyn in the leadership elections of 2015 and 2016, but the leadership issue is settled. Our country’s relationship with the EU is more important to me than the leader or our party, which was why Jeremy and I decided it was best for me to leave the Shadow Cabinet when I could not agree with his position on the EU back in 2015 (his position has thankfully changed since then).

I am part-Irish and have Danish, Spanish, French and Irish nationals in my family. In this sense, my family is typical of so many in my constituency of Streatham, which scored the highest Remain vote in the referendum. For us, this is not just political but deeply personal.

We in Streatham are proud to be British and European, and we cannot bear the direction these Brextremists are taking us. Now is the time for us to all stand up and be counted, and to fight for the open, inclusive Britain we want our country to be. The risks and dangers posed to our democracy are too great for us not to do so.