Tory rebel Dominic Grieve was accused of ‘supping with the devil’ last night after he held secret talks with avowed enemies of Brexit.

He was spotted slipping into the European Commission’s Smith Square HQ in London yesterday for a private meeting of campaigners set on reversing the result of the referendum.

Attendees included Tony Blair’s former spin doctor Alastair Campbell and Tory and Lib Dem peers who have rebelled over Brexit. Also present were leaders of People’s Vote, which campaigns for a second referendum, Open Britain, the successor organisation to the official Remain campaign, and Best for Britain, the anti-Brexit group backed by financier George Soros.

Tory rebel Dominic Grieve (left) was spotted heading into the European Commission's building with Alastair Campbell (right) yesterday

Jacob Rees-Mogg, a leading Tory Leaver, said last night: ‘Dominic should be careful about the company he keeps if he wishes to maintain his position that this is not about stopping Brexit.

‘He is someone I trust and when he says he is not trying to frustrate Brexit I believe him but the people he is associating with are clear they do want to stop Brexit.

‘If you sup with the devil you should use a long spoon and he is using an egg spoon.’

The Smith Square EU building, which is a short walk from Parliament, was once Tory Central Office and the scene of Margaret Thatcher’s election triumph of 1979. But it was sold to the EU in 2007 and is now called Europe House.

An agenda for the ‘Where Next for Brexit?’ meeting was marked ‘in confidence’ but seen by the Mail. It says: ‘This informal forum connects the main operational UK pro-EU organisations and individuals and meets under the Chatham House Rule.’

This rule holds that the discussions should not be made public.

Mr Grieve was expected to talk about the EU Withdrawal Bill, which caused parliamentary turmoil this week.

The QC and former attorney general led a group of 13 Tory MPs who forced Theresa May into making concessions on Tuesday evening.

Despite insisting they are not trying to reverse Brexit, the MPs are threatening to back a House of Lords amendment that would make it impossible to leave the EU without a ‘deal’. It would also put Parliament in charge of the final stage of the negotiations. Minutes after Mr Grieve left yesterday’s meeting the participants started planning on a campaign for a second referendum to stop Brexit.

Mr Rees-Mogg said it was ‘completely improper’ for the Commission to allow its buildings ‘to be used in a domestic political controversy’.

‘We fund the EU and it should not use our money to interfere in our domestic affairs,’ he said.

Sir Bill Cash, the chairman of the Commons European scrutiny committee, said: ‘It’s clear that Mr Grieve is consorting with those people who are all intent on reversing Brexit.

‘It makes his claim that he is trying to be helpful to the Government transparent nonsense.’

Former Tory leader Iain Duncan Smith said: ‘I’m surprised if he is meeting with a whole load of people whose sole purpose is to stop Brexit when he has said it is not his intention to do so.’

A secret meeting of Pro Euro rebels at Europa House in Westminster

A senior ministerial source said: ‘This is clear evidence that a certain group of MPs will stop at nothing to keep us in the EU.’

Mr Grieve said it was ‘rubbish’ to suggest the meeting revealed his true intentions. He also claimed the invitation was made ‘a long time ago’.

‘They asked me to go along and explain something about what was going on in Parliament, just as I go and talk to all sorts of groups,’ Mr Grieve said.

‘If I was invited by an audience that was interested in the issue that were Leavers I would go as well. We live in a democratic country where people engage with all sorts of people.’

The revelations came on another day of drama in Westminster during which:

Theresa May was locked in talks with Mr Grieve and other Tory rebels over their demand that MPs should be given the power to ‘direct’ Brexit policy, which critics claim could lead to the UK staying in the EU;

Leading Conservative Remainer Anna Soubry warned MPs it was time to tell leave voters to ‘suck it up’ and accept that Britain was staying in the single market and would have to accept free movement;

Six Labour MPs resigned from the front bench to vote to keep Britain in the single market, as Jeremy Corbyn suffered a major rebellion over the issue;

Reports claimed that Miss Soubry and Labour MP Chuka Umunna have used cross-party anti-Brexit talks to discuss the formation of a new party called Back Together;

Eurosceptic Tory Daniel Kawczynski urged voters to ‘hold to account’ rebel MPs trying to thwart Brexit;

CBI chief Paul Drechsler warned parts of the car industry would become ‘extinct’ unless the UK stayed in the customs union.

Tory rebels plot with Blair's bullyboy at Maggie's old HQ Pictured (from left to right) Patience Wheatcroft, Ros Altmann and Sarah Ludford pictured in Smith Square yesterday The ex-editor ‘We have to stop Brexit,’ is view of former newspaper editor Patience Wheatcroft, ennobled by David Cameron in 2010. She has claimed in the Lords that ‘the public wants a vote on the final deal’ – a second referendum she hopes will delay Brexit – and has encouraged Remainers, saying ‘history is on your side’. Pensions queen A Tory peer since 2015 and a former pensions minister under David Cameron, Ros Altmann has repeatedly voted against the Government on key Brexit issues in the Lords. A regular on TV, the pensions and elderly rights campaigner has threatened to leave the Conservative Party if it pursues a hard Brexit. The Lib Dem MEP A former Islington councillor, Sarah Ludford was given a peerage in 1997. Managed to ‘double up’ for 15 years by also being a Member of the European Parliament. Now the Liberal Democrats’ Brexit spokesman in the House of Lords, from where she has led the party’s fight to keep Britain in the EU. Pictured (from left to right) Henry Porter, AC Grayling and Lord Hugh Dykes The sore loser Former Observer columnist and deeply embittered Remainer Henry Porter. Before the referendum he wrote he would be a ‘very sore loser if we came out’ and ‘in mourning for a project that was as brave and beautiful as anything in European history’. True to his word, he still campaigns against Brexit. The non-believer Philosopher and atheist AC Grayling said the Government’s attempt to trigger Article 50 – and begin our departure – without consulting Parliament amounted to ‘a kind of coup’ and called for a general strike. ‘The effort to talk about ...what’s going to happen after Brexit is an attempt to normalise acceptance of leaving the EU,’ he said. The arch-defector A Tory MP for 27 years and minister under Ted Heath, Lord Hugh Dykes joined the Lib Dems in 1997 after Ken Clarke lost his leadership bid and became an adviser to Paddy Ashdown on EU affairs. He is vice-president of the British-German Association and holder of the German Federal Order of Merit and French Legion d’Honneur. Picture shows (left to right) Tom Baldwin, James McGrory, Unknown woman and Alistair Cambell leaving a secret meeting in Europa House Far left: MIliband’s Spin chief Yet another famously foul-mouthed Labour spin doctor, Tom Baldwin was director of communications when Ed Miliband was party leader. Earlier this year he took a role with the ‘People’s Vote’ campaign which is demanding a second referendum on Brexit in an attempt to reverse the result. Second left: Nick Clegg’s sidekick Former spin doctor for Nick Clegg when he was Lib Dem leader, James McGrory moved to the official Remain campaign, Stronger In, where he was co-executive director. After the referendum he became a board member at Open Britain, the Roland Rudd-funded anti-Brexit campaign group where Peter Mandelson is also a board member. Far right: Crude voice of Blairism Tony Blair’s notoriously foul-mouthed former spin doctor Alistair Campbell is, like his former boss, utterly determined to stop Britain leaving the EU. Was forced to apologise last year after comparing Brexit supporters to jihadi extremists. The woman at the centre is unidentified Advertisement

Mr Campbell was seen entering Europe House shortly after 10.30am yesterday. Mr Grieve followed just before 10.45am. Shortly afterwards came Tom Baldwin, who was Labour ex-leader Ed Miliband’s spin doctor and now works for People’s Vote, and James McGrory, the former communications director at Stronger In, the official Remain campaign, who now works for Open Britain.

Mr Grieve left just before midday. Most of the other participants left around 1pm, including Baroness Altmann, the anti-Brexit Tory peer, Patience Wheatcroft, the Tory peer and former newspaper editor who has backed a second referendum and has argued ‘we have to stop Brexit’, and the Lib Dem Brexit spokesman in the Lords, Sarah Ludford.

They were joined by AC Grayling, the philosopher who has said it was wrong to ‘normalise acceptance of leaving the EU’.

The meeting reveals that separate Remainer groups are coordinating to try to stop Britain’s departure from the EU. On Tuesday night Mr Grieve told the Commons he was not trying to prevent Brexit but ‘legitimately looking at the detail of one of the most complex legal and political exercises in which we have ever engaged in peacetime’.

In an interview with The Guardian last month, he backed another national poll to ask the public ‘is this what you really want?’ but also claimed he was ‘not working to precipitate it’.

Prime Minister Margaret Thatcher, with husband Denis, wave to the crowds form the Conservative central office in Smith Square,

Last night he rebelled against the Government to vote in favour of Britain joining the European Economic Area, which would mean staying in the single market.

A Commission spokesman said it did not organise the Smith Square meeting and suggested it may have been booked by an MEP who can use rooms in the building for free.

The spokesman confirmed that no Commission officials attended the meeting.

A spokesman for ‘Where Next for Brexit’ said: ‘Pro-Europeans meeting to discuss Europe and inviting pro-European guest speakers should not surprise anyone.

‘It is extraordinary that this should be regarded as a news story.’

Mr Umunna’s calls for a new party, reported by the New Statesman, were made at a meeting of a Pro-Remain grassroots campaign group.

A source told the magazine: ‘He came in, huffing and puffing, saying that he’d had enough of Labour’.

Miss Soubry has reportedly told fellow MPs ‘Chuka and I are looking at what the future brings’.