The Brexit deal has been agreed and the ERG’s ‘star chamber’ of Brexiteer lawyers have given it their seal of approval. Today parliament is expected to pass the deal and the document is now on an RAF plane accompanied by UK and EU officials ready to be signed by the PM in a matter of hours. Thus ends, to a large extent, a running sore in the Conservative Party between the leadership and their eurosceptic colleagues and followers.

Sir Bill Cash, who led the team of lawyers looking into the deal, said the ERG would “continue to be an incredibly important part of this muscular role to drive the project forward” but added “If you look back where we were on 12 December it’s an incredible leap into a completely new sovereign dimension. We’ve moved the whole argument in the space of a year.” One senior member of the ERG said it was “the completion of a revolution, as important constitutionally as 1688, the restoration of sovereignty and a reversal of a process that would see us subsumed into a superstate.”

But they haven’t kept all of their allies on side. Last year the ERG decisively broke with the DUP when they voted to impose a border down the Irish sea as part of Boris Johnson’s Withdrawal Agreement. There will be no vote of solidarity with their fellow Brexit warriors today – who were indispensable to Theresa May’s deal being defeated – as the ERG approves a deal which does nothing to modify the arrangements which keep Northern Ireland subject to EU law on 1 January. The price of Brexit for Great Britain has been BRINO, at the very least, for loyal Ulster. It also, keen-eyed unionists note, makes Nicola Sturgeon’s job a lot easier if the pro-union side can’t make lurid claims about what a separate Scotland’s EU frontier border with what’s left of the UK would entail. Michael Gove, who cast aside his previous sympathy for Ulster’s Unionists to make this deal, has not done Scotland’s any favours either.

Fishermen are also calling the deal a sell-out because it returns a comparatively small amount of fish to the UK and retains several aspects of the environmentally disastrous Common Fisheries Policy. For the ERG their work for now is done, the focus is on Tory unity not division.

But considering their history it seems unlikely that they will put down their spears forever. The ERG have already fought against two Conservative Prime Ministers in recent years and played a large part in the resignation of both of them. Of course, they weren’t always plotting to remove the leadership, there was a time when the Tory front bench benefited from their support. Their research even helped to get David Cameron into power.

The key attraction for ERG membership was the top quality research and the wide range of acceptable views

Long before the referendum David Nuttall, a former Treasurer of the ERG, says the key attraction for membership, which included paying toward the cost of a researcher, was the fact that the research papers were of such high quality and that it was a broad church. For most of its history the ERG resisted becoming an ideologically narrow group specifically calling for the UK to leave the EU. This put some people off – Shipley MP Phillip Davies preferred to lend his support to the Better Off Out campaign which was explicitly calling for the UK to leave – but it was the broad appeal that meant it could boast such high membership numbers, and the fact that it could count the likes of John Bercow and David Gauke as notable europhile-to be alumni. Gauke, who lost his seat for being anti-Brexit, was once the ERG’s treasurer.

As Gordon Brown drove the Lisbon Treaty through the Commons in the late 2000s the ERG’s then researcher Robert Broadhurst provided ammunition to criticise the Labour Government over their ratification of yet another wide-ranging EU treaty. Most Conservative MPs were broadly eurosceptic but lacked detailed knowledge about the EU or a clear plan about how to deal with it. But Broadhurst’s briefings changed this and helped to galvanise a better informed, and better armed party. It also attracted the attention of David Cameron who turned ERG briefing notes into attack lines against Labour.

But the alliance between David Cameron and his backbench eurosceptics began to break down in 2010 when he became PM, despite the support they had given him during the opposition years. Broadhurst had even been named Dods Conservative Parliamentary Researcher of the Year for his work briefing the front bench on the Lisbon Treaty but sadly for Cameron the group didn’t pack up once the Tories had got into government. In 2010 the ERG Chair David Heathcoat-Amory lost his seat and the role was taken by an MP from the new intake, Chris Heaton-Harris. If the Government thought a freshman MP would mean an easy life, they were wrong. In the autumn of 2010 the EU announced an increase in the size of member state contributions to the budget. The ERG stoked dissent by circulating a briefing note translating the monetary increase into the number of nurses, teachers and soldiers it could pay for if the UK vetoed it.

David Nuttall’s referendum debate was a watershed moment

Alongside frequent briefing papers undermining support for membership, one event can legitimately be described as the watershed moment. In 2011 David Nuttall, thanks to the new backbench business committee, proposed a motion calling for a referendum on whether the UK should stay in the EU, leave it or renegotiate its membership. The BBBC filled the big gaps in parliamentary time due to the coalition Government’s slim agenda and the eurosceptics exploited it. Nuttall said: “People regarded us as nutcases when I had my debate. It was ‘give them their day in the sun and they’ll go away’, but then 80 odd Tories voted against the three line whip and the rest is History”. 83 Tories voted in favour, making it the largest eurosceptic faced by a Government up to that point. Much went into this rebellion, not least disquiet at the very narrow moderniser clique running the party under Cameron, Osbourne and Gove. But it also represented an attack on the modernisers for having failed to win a majority against Gordon Brown’s imploding Government, then the most unpopular on record. However, and tellingly, the cause people looking to attack the leadership could unite behind was Europe.

The rebels formed an APPG on an EU referendum and the momentum from the vote led to David Cameron’s Bloomberg speech in 2013 where he pledged to hold an in/out referendum if he won the next election. “Staying in the EU wasn’t the choice of the Status Quo” says Nuttall. “Every single development was all one way, it was never a case of powers flowing back”.

David Cameron did win the next election in 2015 – though none of his immediate circle expected him to – and therefore was unexpectedly obliged to keep his referendum promise. Something George Osborne feared but which Cameron, tired of eurosceptic cranks and gadflies, trusted to his gambler’s luck to solve.

Just one year earlier UKIP had won the European Elections which bolstered the ERG’s force of arguments internally. Armed with new researcher Christopher Howarth, previously of Rodney Leach’s Open Europe and before that working for the then Shadow Europe Minister, Mark Francois, the group continued plotting against the government to make the now looming referendum as fair as possible.

With just months to go before the actual plebiscite, Bill Cash, Bernard Jenkin and Steve Baker (who would lead the ERG by the end of 2016) prevented David Cameron from keeping purdah as short as possible, as the Government has sought. Purdah rules kick in before a general election or referendum and mean the government can no longer campaign or use its resources to try to influence the vote. Paul Stephenson, director of communications for Vote Leave said they would have been “screwed” with a short purdah. In all the many small cumulative parliamentary victories Tory backbench Brexiteers won in the 2015 parliament, they were greatly assisted by both Cameron’s small majority and the support of the DUP’s avowedly withdrawalist MPs.

ERG members also won a key battle in cabinet. David Cameron was insistent that Cabinet collective responsibility must be maintained, which would have left Cabinet Brexiteers like Iain Duncan Smith, Chris Grayling and Theresa Villiers sitting on their hands whilst their Cabinet colleagues could articulate the government’s ‘Remain’ policy. But after Grayling threatened to resign and Villiers was also rumoured to be on the verge of quitting, Cameron was forced to allow heavy hitters in his cabinet like former party leader IDS the ability to campaign for Leave.

But the ERG only became well-known outside of Westminster when it began pressuring and ultimately rebelling against Theresa May. Whatever they thought of the tricks he played during the referendum, ultimately they saw David Cameron as more straightforward than his unknowable, unclubbable successor. He campaigned for Remain in the referendum and resigned when it didn’t go his way. It was Theresa May, the half-hearted Remain campaigner turned Boudicca of Brexit that they found more infinitely more tricky than the former PR man turned PM. She promised them everything they wanted whilst concocting an EU deal behind the  back of DExEU that ultimately led to dozens of resignations.

The Chequers Plan, revealed to the Cabinet (including the Brexit Secretary) at the Prime Minister’s country house in July 2018, included such horrors for Brexiteers as a “common rulebook” with the EU and a “facilitated Customs arrangement” resting on a permanent Northern Irish backstop. The UK would follow EU rules it would have no say on and have its trade policy and access to the single market managed in Brussels.

Gradually though, Brexiteers inside and outside parliament began to begrudgingly support it despite the rising poll ratings for Nigel Farage’s new Brexit Party. Theresa May finalised her Withdrawal Agreement with the EU and tried to pass it through the House of Commons, ultimately failing three times. But each time the numbers of eurosceptics voting against fell and the pro-Brexit media turned against those who were holding out. Various commentators called the remaining ERG ‘spartans’ things like “wreckers” or “Remain’s useful idiots”.

The organisation skills of ERG chair Steve Baker were crucial at this point. He coordinated the rebellions with a vast array of WhatsApp groups and broadcast lists which he used to sooth feathers and cajole members in equal measures. But so too was his unquestioned integrity vital.

In the final meeting of ERG parliamentarians before the fateful third meaningful vote (MV3) on Theresa May’s deal in March 2019, Baker told a packed committee room why he would not vote for the deal that they had all come under such pressure to back:

What is our liberty for if not to govern ourselves?

Like all of you I have wrestled with my conscience about what to do.

I could tear this place down and bulldoze it into the river. These fools and knaves and cowards are voting on things they don’t even understand. We’ve been put in this place by people whose addiction to power without responsibility has led them to put the choice of No Brexit or this deal. I may yet resign the whip than be part of this.

One source present said the speech was “spellbinding” and “absolutely critical” because it increased the number of Spartans and this stopped Theresa May risking another vote.

David Nuttall lost his seat in Theresa May’s 2017 election gamble but says he probably would have voted for Theresa May’s deal had he been an MP at the time. In hindsight, however, he believes the spartans made the right decision. He said his rule of thumb had always been to vote in the most eurosceptic way possible but that it was difficult to tell what that was during the fraught days of early 2019 with a hung parliament and a rogue speaker who was allowing time for Remainers to pass their own legislation. In the end 28 Tories defied the pressure and voted against Theresa May’s deal, an act that ultimately led to her resignation and a new Prime Minister. Was their final rebellion a calculated act or sheer bloody-mindedness? Nuttall says it’s the former: “Steve Baker is a very very clever and accomplished guy, he’s nobody’s fool. I don’t think they just got lucky, there’s a real argument for saying that they achieved what they achieved through their own efforts.”

That the Brexit we have today isn’t the deal Theresa May and Olly Robbins negotiated isn’t down to Vote Leave figures like Boris Johnson and Michael Gove, both of whom voted for it. Instead, for better or worse, we’re living in the world Spartans like Baker, Braverman, Villiers, Patel, Jones and Francois made.