The six Cabinet rebels voting for Britain to leave the EU have been banned from using any government material or resources to campaign for Out, under strict new rules published today.

Jeremy Heywood, the Cabinet Secretary, sent a letter to all civil servants this morning telling them that government resources must only be used in the referendum campaign if it supports the Government's official stance in support of Britain's membership of the EU.

It risks causing further anger among Tory Eurosceptics as it will put pro-Brexit ministers at a significant disadvantage to pro-EU members of the Government in the run up to June's referendum.

Justice Secretary Michael Gove, left, arrived at Cabinet this morning for the first time since it emerged he would defy David Cameron to back the Out campaign. Employment Minister Priti Patel, also pictured arriving at Cabinet, is also backing Brexit. The pair are banned from using the civil service to support their EU arguments

Other Brexit rebels, including Iain Duncan Smith, left, John Whittingdale, centre, and Theresa Villiers, right, all appeared in Downing Street this morning. Under the Civil Service guidance on the EU referendum sent by the Cabinet Secretary Jeremy Heywood today, they will all be at a disadvantage against their pro-EU colleagues

It means Michael Gove, Iain Duncan Smith, Priti Patel, Theresa Villiers, Chris Grayling, John Whittingdale and around 15 junior ministers are barred from accessing official department papers that support their case for Britain to leave the EU.

The rules will also apply to their advisers, who must only campaign for Britain to leave the EU in their spare time.

They will be unable to provide their ministers with briefing notes or speech preparation to make the case for leaving the EU but can use the same kind of resources to help ministers on the opposite side of the argument.

But at the same time ministers and advisers who back Britain staying in the EU are free to use government papers and other resources to support their case.

It came on a day when Mr Cameron attempted to regain control in the EU referendum campaign after a bruising day of angry clashes with his own party in the House of Commons yesterday, including his friend Boris Johnson, who is among those campaigning to leave the EU.

The party's former leader William Hague today warned Tory ministers facing a bitter divide over Europe not to destroy the party so it cannot win in 2020.

Jeremy Heywood, the Cabinet Secretary, sent a letter (pictured) to all civil servants this morning telling them that government resources must only be used in the referendum campaign if it supports the Government's official stance in support of Britain's membership of the EU

The key paragraph announcing the ban on the use of government material for pro-Brexit arguments (pictured) rules that civil servants must not provide pro-Brexit ministers with information that supports their case to quit the EU because it goes against the Government's official position to remain a member of the 28-state bloc

He also said ministers should only campaign in their spare time - hours before David Cameron embarked on his first 'national tour day' to make the case for staying in the EU.

The guidance sent to civil servants today seeks to ensure that ministers and civil servants abide by David Cameron's decision that the Government's official position will be to stay in the EU and ministers who 'take a different personal position' may argue against that position only outside of their official government role.

The key paragraph announcing the ban on the use of material for pro-Brexit arguments states: 'As set out in the Prime Minister’s letter it will not be appropriate or permissible for the Civil Service to support Ministers who oppose the Government’s official position by providing briefing or speech material on this matter.

Home Secretary Theresa May, seen arriving for today's Cabinet meeting, boosted Mr Cameron by backing his campaign to keep Britain in the EU. She will be able to access official government material to make the case for staying in the EU - unlike her anti-EU colleagues

'This includes access to official departmental papers, excepting papers that Ministers have previously seen on issues relating to the referendum question prior to the suspension of collective agreement. These rules will apply also to their special advisers.'

Civil servants and ministers who breach the rules are likely to face disciplinary action. Asked what the consequences of breaking the code would be, the Prime Minister's official spokeswoman said: 'Let's cross that bridge when it happens.'

Sir Jeremy also said that special advisers who want to work for a campaign team must seek the Prime Minister's approval.

If they want to work full-time on a campaign they will have to resign their positions for the duration of the referendum, and their Government salary will be cut to reflect any part-time work for a campaign.

The instructions came after David Cameron suspended the principle of collective responsibility on Saturday to allow ministers to campaign against the Government position of supporting continued UK membership of the EU.

Clarifying the reasoning behind the strict code of practice governing the civil service during the EU referendum, the letter states: 'As previously agreed, and confirmed at Cabinet, individual Ministers will be able to take a different personal position from that of the Government on the issue of the EU Referendum.

'This wholly exceptional arrangement applies only to the question of whether the UK should remain in a reformed EU or leave.'

The five-page letter also warns civil servants that government publications will be 'scrutinised even more closely than usual' in the run up to the referendum and tells employees to take extra care to ensure publications are accurate.

Mr Heywood writes: 'We can expect government publications to be scrutinised even more closely than usual and so it is especially important that the usual propriety principles of good administration are applied to ensure that material for publication is accurate, with facts and evidence clearly sourced wherever possible.'

THE MAGNIFICENT SEVEN: WHAT THE TOP TORIES BACKING BREXIT SAY ABOUT BRITAIN'S MEMBERSHIP OF THE EU By dramatically backing Brexit last night, Boris Johnson has joined six Cabinet rebels, who were finally free to speak their mind on the EU at the weekend. The - 'freedom fighters' - as they have been dubbed by admirers - are: BORIS JOHNSON The London Mayor finally came off the fence last night, ending months of speculation over which side of the referendum campaign he would join. Mr Johnson invoked the glories of the British Empire and the leadership of Winston Churchill to say the country which gave the world parliamentary democracy should not subject itself to 'legal colonisation' from the EU. 'This is a once in a lifetime chance to vote for real change in Britain's relations with Europe. This is the only opportunity we will ever have to show that we care about self-rule. 'A vote to Remain will be taken in Brussels as a green light for more federalism, and for the erosion of democracy.' MICHAEL GOVE The Justice Secretary is one of David Cameron's closest friends - he was part of the 'kitchen cabinet' who encouraged him to run for the Tory leadership - and his decision to join the Out campaign on Saturday was the first major blow for the PM. In a 1,500-word essay explaining his decision to leave the EU, which he described as 'mired in the past,' Mr Gove wrote: 'Far from providing security in an uncertain world, the EU's policies have become a source of instability and insecurity.' IAIN DUNCAN SMITH Few people were surprised by Iain Duncan Smith's decision to back the Out campaign: the Work and Pensions Secretary has been a long-standing critic of the EU and supporter of tighter immigration controls. But yesterday he directly contradicted David Cameron's claim that Britain was 'safer and stronger' in the EU by claiming staying in the EU would make Britain more vulnerable to a Paris-style terror attack. And savaging the PM's EU deal, Mr Duncan Smith wrote in today's Daily Mail: 'The truth is that there is nothing proposed in last Friday's agreement that reduces or returns the enormous powers that the Commission and the Court of Justice have over our national government.' Priti Patel The employment minister is regarded as the up-and-coming poster girl for Cabinet Eurosceptics. Her decision to join the Out camp was no surprise but her popularity with Tory grassroots will deal a blow to the PM. She has railed against the 'democratic deficit' of the EU's institutions, adding: 'My experience in business is that organisations are only successful and efficient when they are accountable and flexible – and the EU is neither.' JOHN WHITTINGDALE The Culture Secretary is the last authentic Thatcherite in the Cabinet: in the 1980s he worked as her private secretary and has remained loyal to her ideology – including her Euroscepticism – since. At the weekend he called for Britain to 'recover the powers we have lost' and said Cameron's pledge to reduce net immigration to the tens of thousands would be 'impossible' while remaining a member of the EU. CHRIS GRAYLING Mr Gove's predecessor as Justice Secretary, Chris Grayling is a long-term Eurosceptic. The Manchester United fanatic was deployed by the Tories as an energetic 'attack dog' during their long period in Opposition, harrying Labour – including the Blairs – over their personal business affairs. The 6ft 5in Leader of the House has a cool relationship with Gove, who has reversed many of his justice reforms. THERESA VILLIERS The Northern Ireland Secretary has long backed quitting the EU and made her views clear straight after Saturday's Cabinet meeting. She said she will vote to leave the EU 'to take back control over our country and making our laws and controlling our borders'. The six Cabinet ministers - who make up a sixth of David Cameron's top team, are joined by around 15 junior ministers, some of whom will play a prominent role in the Conservative party's future. Among the most high profile of the pro-Brexit junior ministers are: Penny Mordaunt Armed Forces minister Penny Mordaunt, pictured at Downing Street after being given a promotion last May, said she was backing Brexit because it was the only way to guarantee national security The Armed Forces minister shot to prominence after she starred on the primetime TIV diving show Splash with Tom Daley two years ago. She will be arguing against her direct boss - the Defence Secretary Michael Fallon, who has set out his firm belief that staying in the EU is the best way to guarantee national security. Julian Brazier He is another defence minister who has come out in favour of Brexit. He is in charge of the Reserves and said three things had persuaded him to campaign for Britain to leave the EU: the financial crisis in the eurozone, the 'torrent of people in Europe' who could be heading to the UK and his desire to regain sovereignty for the British Parliament. James Wharton The 32-year-old minister in charge of the Northern Powerhouse was tasked with the original effort by Tory MPs to secure an EU referendum by introducing a Private Member's Bill to Parliament as earlier as 2013. Mr Wharton, who surprised pollsters by extending his majority in the north east seat of Stock-on Tees in last year's election, announced on Facebook he was backing Brexit, saying: 'We should look to the world, not just the EU'. Andrea Leadsom The energy and climate change minister announced she will be campaigning for Britain to leave the EU. She wrote on her website: 'I want to be absolutely clear – I will be voting to leave the EU. 'This is not a decision that I have made quickly or easily, as I have been a strong advocate for reform within Europe for many years.' George Eustice The farming, food and marine environment minister is one of the founding members of the EU Fresh Start group - made up of 2010 and 2015 intake MPs today to campaign for Brexit. Mr Eustice campaigned against the UK joining the euro and in 1999 he stood as a Ukip candidate for the European Parliament elections. James Duddridge The foreign office minister is another government figure defying his departmental chief - the Foreign Secretary Philip Hammond. Advertisement

Cameron loyalist William Hague demands the Brexit rebels only campaign in their spare time - as the PM heads out of London to sell his deal to voters

It came as William Hague today warned Tory ministers facing a bitter divide over Europe not to destroy the party so it cannot win in 2020.

Lord Hague said ministers should only campaign on their spare time - hours before David Cameron embarked on his first 'national tour day'.

He said as well as doing their day jobs, both sides should ensure they 'praise each other's achievements'.

David Cameron, seen in Downing Street yesterday, is due to hit the EU campaign trail later today while Labour's referendum leader Alan Johnson, centre, will warn about the risks to manufacturing. Lord Hague today said the Tory Party should not tear itself apart

Lord Hague's intervention came as Mr Cameron's Cabinet met for the first time since the referendum campaign officially began and Boris Johnson joined a string of ministers in backing a Brexit.

Lord Hague's intervention, in a regular Daily Telegraph column, came as it emerged via the BBC that Mr Cameron plans two or three events every week to sell his EU campaign to the voters.

Following a Cabinet Mr Cameron will visit a business in Berkshire today as he attempts to move his campaign out of Westminster.

Lord Hague today said: 'They should campaign in their spare time and keep on governing every day as the taxpayer who pays them expects them to do.

'The flow of policy and announcements on other subjects should not stop.

'Around the globe, people now acknowledge that the UK is delivering the best performance of the advanced economies.

'There's a big Budget coming up and Conservatives all need to get behind it.'

ALMOST 200 FIRMS BACK THE PM - BUT SOME OF HIS CLOSEST ADVISERS AND BRITAIN'S BIGGEST NAMES STAY SILENT Mr Cameron was backed by 197 businesses today The majority of Britain’s biggest companies have refused to sign a letter backing membership of the European Union. High street shops including Sainsbury’s, Tesco and Next and banks such as Lloyds and Royal Bank of Scotland did not put their names to the letter published today. It had been suggested that bosses of 80 of the FTSE 100 firms would sign the pro-Brussels letter, but in fact only 36 have done so. Those who signed include multi-national corporations such as HSBC, BAE Systems, BT, Royal Dutch Shell, Rio Tinto and BP, and the chief executives of Heathrow and Gatwick. Even some of David Cameron’s own business advisers refused to sign the letter to The Times which claims that quitting the Brussels club ‘would put the economy at risk’. Yesterday Mr Cameron angrily defended Downing Street’s involvement in orchestrating the pro-EU letter after it emerged that it was drafted by a civil servant. The Prime Minister has been trying to rally support from major businesses to endorse his deal to keep Britain in the EU ahead of the referendum on June 23. But several of them have backed people power to decide for the nation. Others that refused to sign the letter include Primark owner Associated British Foods, insurer Legal & General and investment firm Hargreaves Lansdown, whose founder Peter Hargreaves is a loyal Thatcherite. It is thought an eight-sentence template letter was sent to firms at the weekend by Downing Street adviser Chris Hopkins. Advertisement

Lord Hague warned ministers who fight out personal 'feuds' during the referendum should find themselves without a Government job at the end - but said those who campaign fairly should be embraced by the Prime Minister following the result.

And Lord Hague also suggested after the referendum campaign comes to an end after June 23, Tory MPs should all go away for a 'bonding' session to swap war stories.

He said: 'They can do so bearing in mind that they represent our governing party, and one to which there is absolutely no alternative.'

Elsewhere in the referendum campaign, former Labour home secretary Alan Johnson will warn of the danger to manufacturing jobs from a Brexit.

At a speech, the leader of Labour referendum campaign warned: 'For UK manufacturing jobs, our EU membership is absolutely critical. Two thirds of British jobs in manufacturing are dependent on demand from Europe.

'That's two thirds of our manufacturing base reliant on that single market access and Britain's membership of the EU.

'That's over one and a half million manufacturing jobs here in Britain.

'And turning specifically to apprentices in the manufacturing industry, and I'm pleased to see some of you here today, around 50,000 apprentices work today in manufacturing apprenticeships that depend on trade linked to our EU membership.

'That's 50,000 apprenticeships which depend on our EU membership and leaving the EU could put those at risk.

'For each one of those apprentices, gaining skills, earning a good wage and working towards a career, we can't let them down, turn our back on the world and cut British manufacturing and industry off from their largest export market.'

Vote Leave dismissed the claims, issuing a statement from Christopher Nieper, the managing director of clothing manufacturer David Nieper Ltd.

He said: 'One third of our customers are within the EU and I’m confident they’ll continue to choose our British manufactured fashion regardless of a Brexit and we are hiring more manufacturing apprentices to keep up with demand.

‘The EU is no longer where the growth is. In 1980, the 28 nations who are now the EU members represented 30 per cent of the world gross product, this has now fallen to below 17 per cent.

'The bigger opportunity for British companies is now amongst the emerging economies of China and India alongside America and the commonwealth countries.

‘In order to stop sending £350 million to Brussels every week and take back control of our trade deals, our economy and our borders we should leave the EU. It's the safer option'

The new referendum exchanges comes a day after Mr Cameron and Boris Johnson clashed angrily in the House of Commons.

Mr Johnson, who declared for Brexit on Sunday night, has no plans to take up a formal role with the Vote Leave campaign but his interventions will hurt Mr Cameron's battle to keep Britain in the EU.

In tense exchanges at the Despatch Box yesterday, Mr Cameron declared: ‘I’m not standing for re-election.

‘I have no other agenda than what is best for our country.’

Shaking his head, Mr Johnson responded: ‘Rubbish, rubbish.’

One observer said the parliamentary exchange was jaw-dropping; another described it as the most savage ‘blue on blue’ clash since Geoffrey Howe took on Margaret Thatcher in 1990.

Mr Johnson has faced claims that he does not want to leave permanently. Rather, his critics said, he wants to lead Britain out of the EU then back in again, but on better terms.

The mayor denies this. But Mr Cameron said: ‘On diplomacy, the idea that other European countries would be ready to start a second negotiation is for the birds.

‘I have known a number of couples who have begun divorce proceedings but I do not know of any who have begun divorce proceedings in order to renew their marriage vows.’

No 10 sources strongly denied the divorce remark had been aimed at Mr Johnson, who is on his second marriage.

Labour MPs delighted in the PM’s attack, crying ‘more, more’. Mr Cameron referred to them as his ‘new friends’.

Mr Cameron later attended a 30-minute meeting of the Tory 1922 Committee. Steve Baker MP suggested the PM had succumbed to a ‘moment of high drama’ over Mr Johnson.