David Cameron speaking at the Mansion House in London today. A pact between the PM and big business has been exposed

Boris Johnson called for an inquiry into what appeared to be 'collusion' after it emerged that David Cameron secretly plotted with big business to fight Brexit.

The former London Mayor said the revelation showed Mr Cameron's EU renegotiation bid was 'fiction' as he had already decided to campaign for a remain vote.

The secret ‘mobilisation’ plan involved asking FTSE 500 companies to put in their annual reports warnings about the dangers of Brexit.

The strategy was discussed in a letter from Serco boss Rupert Soames to Mr Cameron 11 days before the latter’s renegotiation deal with the EU was complete. This followed a meeting a few days earlier.

The PM had been telling the Commons that he ‘ruled nothing out’ unless he won concessions from the EU.

Responding to the claims today Mr Johnson said they made Britain look like a 'banana republic'. Serco has multi-billion-pound contracts with the Government.

'This is the biggest stitch up since the Bayeux Tapestry,' Mr Johnson said. 'It stinks to high heaven. FTSE 100 chiefs are seeing their pay packets soar while uncontrolled immigration is forcing down wages for British workers.

'Now we learn that some fat cats have been secretly agreeing to campaign for remain while angling for lavish Government contracts. It makes us look like a banana republic. And it is also now beyond doubt that the so called renegotiation was a fiction designed to bamboozle the public. It was a meaningless mime, a ritual, a kabuki drama in which the outcome was utterly preordained. This is not the far-reaching and fundamental reform we were promised.'

In another frantic day as the referendum battle heats up:

Lord Heseltine accused Mr Johnson of behaving ‘irresponsibly and recklessly’ and said he would be surprised if he became PM;

Mr Johnson warned that the government's living wage was having a 'magnetic' effect on migration from Europe;

Mr Cameron claimed that both the leader of Islamic State and Vladimir would be happy if Britain voted for Brexit;

The CBI business group was accused of being anti-democratic after orchestrating a pro-EU lobbying campaign of 800,000 workers;

Energy minister Andrea Leadsom warned that Britain was being ‘overwhelmed’ by EU migrants.

Nigel Farage has said he wants another referendum to be held unless Remain wins by a huge margin on June 23

Insurance group Lloyds of London has supported EU membership, arguing its business would be severely damaged if we leave

Czech supermodel Eva Herzigova has become the latest celebrity to lecture Britons on which way to vote, saying Brexit would be 'disastrous'

WHAT THE PRIME MINISTER TOLDS MPs ... AS HE SCHEMED IN PRIVATE ‘I am not arguing – and I will never argue – that Britain couldn’t survive outside the European Union. We are the fifth largest economy in the world. The biggest defence player in Europe with one of the most of extensive and influential diplomatic networks on the planet. ‘The question is not could Britain succeed outside the European Union, it is how will we be most successful? How will Britain be most prosperous? How will we create the most jobs? ... How will we be most secure? And I’ve always said the best answers to those questions can be found within a reformed European Union. ‘But let me say again, if we can’t secure these changes, I rule nothing out.’ ‘Thank you for a very useful meeting last week. There were two points I thought I might follow up on. The first is how to mobilise corporates to look carefully at the risks Brexit represents. ‘I am working with Peter Chadlington and Stuart Rose (the head of Britain Stronger in Europe) with a view to contacting FTSE 500 companies who have annual reports due for publication before June and persuading them that they should include Brexit in the list of key risks... ‘During the Scottish referendum campaign we managed to garner a lot of publicity as a series of companies formally stated in their annual reports that independence for Scotland was a major risk.’ TO HOUSE OF COMMONS, FEB 3 LETTER FROM SERCO BOSS, FEB 8 Advertisement

The talks between Mr Cameron and Mr Soames – an EU supporter who is the brother of the Tory MP Sir Nicholas Soames – took place in early February.

A leaked letter Mr Soames sent to Mr Cameron afterwards, dated February 8, reveals the explosive topic of their conversation.

It states: ‘There were two points I thought I might follow up on. The first is how to mobilise corporates to look carefully at the risks Brexit represents.

‘I am working with Peter Chadlington and Stuart Rose (the head of Britain Stronger in Europe) with a view to contacting FTSE 500 companies who have annual reports due for publication before June and persuading them that they should include Brexit in the list of key risks. All public companies are required to set out in their annual report an analysis of key risks.’

Later that month, global security firm Serco was one of 200 businesses to sign a public letter in support of EU membership.

Lord Chadlington is regarded as one of Mr Cameron’s oldest political allies and is the chairman of the Prime Minister’s local constituency association.

Pro-Europeans: Rupert Soames (left) with his Tory grandee brother Nicholas (right)

He donated £10,000 to Mr Cameron personally to fund his 2005 run for the Conservative leadership. He has donated more than £60,000 to the party since then.

Last night, No10 said it did not comment on leaked documents.

The meeting took place shortly before Mr Cameron delivered a speech on February 8 on the need for sweeping prison reform.

Mr Soames argued in the letter that the private sector only having 15 per cent of the prisons market was a ‘wasted opportunity’.

Tory MP Steve Baker said: ‘This is proof that big corporates are being asked to gang up on hard-working British families to try to bully them into staying in the EU. There is a coordinated attempt to use company reports as campaigning documents.’

And Labour Leave campaigner Gisela Stuart said: ‘Today George Osborne accused the Leave campaign of inventing conspiracies. Now we see that David Cameron is knee deep in one.

‘There are serious issues for the Prime Minister to answer. We now know he has been doing deals with businesses to exaggerate the risk of a vote by the UK to leave the EU.

Prime Minister David Cameron (left) and Boris Johnson, as voters trust Mr Johnson to tell the truth about Europe more than they trust Mr Cameron, a new poll revealed yesterday

He must now tell us urgently how many businesses has he cut secret deals with? Who are they and what were they promised in return?’ Mr Baker added: ‘This should come as no surprise – big corporates do well out of the EU because they can afford well-paid lobbyists and lawyers to stitch up the rules.

‘The same cannot be said for hard-working families who have to wait longer for NHS treatment and have seen living standards fall.’

Serco denied there was any link between support for the EU and trying to secure state contracts.

The company said: ‘We have contracts worth around £130million a year with European institutions such as the European Commission and the European Space Agency, and it is part of a strategy to build the business we do with European institutions.

CBI: BOSSES SHOULD TELL STAFF WHAT A BREXIT WOULD MEAN FOR THEIR JOBS CBI chief Carolyn Fairburn said bosses should explain to employees the implications of Brexit on their businesses Businesses should be writing to their employees and spelling out what a Brexit vote would mean for their jobs, the CBI said today. The business organisation, which represents around 190,000 firms, backs staying in the European Union. Microsoft today became the latest firm to follow the advice, writing to all 5,000 of its UK staff advising while the decision is one 'for individual voters to make' Microsoft's view 'is that the UK should remain in the EU.' Vote Leave blasted the CBI's advice and said it was 'highly regrettable' to see 'bosses gang up on staff'. CBI director general Carolyn Fairbairn insisted the move was 'not about telling people how to vote' but rather about responsible business leaders explaining 'what impact a Brexit would have on company growth, their jobs and their communities'. Vote Leave business chief Jon Longworth said: 'This is an anti-democratic abuse of power by the EU-funded CBI which supported the ERM and the single currency. 'Its own business surveys have been condemned as '‘pretty dodgy'’ by the British Polling Council.' Advertisement

We believe that if Britain left the EU, it would be more difficult for us to win EU government contracts, and we regard this as a risk to the business.’

Yesterday, Mr Johnson also attacked big businesses over the way they are lobbying to keep Britain inside the EU.

He said: ‘There is a parade of big businesses coming out from Downing Street signing letters saying that they agree with every jot and tittle of EU regulation.

‘Well, of course they agree with an open-border immigration policy because it means they don’t, for instance, have to worry too much about us getting local people.

‘They think they can just get a steady supply of unskilled or skilled labour from abroad and what is the result?’ Mr Soames, who is the grandson of Winston Churchill, said he would argue ‘ferociously’ for the UK to remain in the EU whatever the result of the PM’s renegotiation.

He was also a signatory to No10’s pro-EU business letter in February this year.

In recent years, Serco has secured contracts worth £3.2billion to run private prisons in England and Wales. It has also won contracts with the Home Office worth £704million to run immigration removal centres and accommodation for asylum seekers.

Since joining the company in 2014, former Eton pupil Mr Soames has been entitled to a salary and pension worth more than £1.1million a year.

He can also pocket an annual bonus of up to £1.275million.

Last night, the Britain Stronger in Europe campaign seized on comments by Daniel Hannan MEP, who sits on Vote Leave’s campaign committee.

Mr Hannan said the UK could adopt a model similar to Switzerland or Norway.

Remain campaigners said this would mean continuing to allow the free movement of EU migrants.

Addressing a World Economic Forum event at the Mansion House in central London today, Mr Cameron set out a series of 'myths' he wanted to bust about how things would be better outside the EU.

Among them was the idea that there could be a 'bonfire' of regulations without the influence of Brussels.

Answering questions from journalists afterwards, the premier expanded on his concerns about security if we were not members of the bloc.

Name checking Isis chief Abu Bakr al-Baghdadi alongside Vladmir Putin as beneficiaries from Brexit, Mr Cameron said:'It is worth asking the question: Who would be happy if we left?

'Putin might be happy, I suspect al-Baghdadi might be happy.

'Our friends around the world are giving us a very clear message, they are saying 'it's all up to you, it is your sovereign choice'.

Czech supermodel Eva Herzigova joins lectures on Brexit

Eva Herzigova starred in the traffic-stopping 1994 'Hello Boys' adverts for Wonderbra

Supermodel Eva Herzigova has become the latest foreign figure to lecture the British people over the EU referendum.

The Czech - known for starring in the 'Hello Boys' Wonderbra adverts in the 1990s - said it would be 'disastrous' if we voted to leave.

The endorsement comes after Abba star Bjorn Ulvaeus waded into the debate at the weekend saying Brexit would make him 'sad'.

International big hitters such as US President Barack Obama have previously sparked fury among leave campaigners by advising the electorate to stick with Brussels.

Herzigova is among more than 30 Czechs who signed an open letter pleading for the UK to stay in the EU.

'Without the British legacy of democratic institutions, entrepreneurial spirit, common sense and pragmatic approach to problem-solving, the West as we know it would be much weakened, politically and spiritually,' it said.

'Britain, under the exit scenario, would fare no better. It would be stranded in the middle of the Atlantic, unable to draw on the synergies of the European project. It would be left alone to deal with the ever-present threats of nationalism, populist politics, migration issues and ethnic intolerance. Closing its doors to workers from the EU, it would have to look for manpower, most likely less qualified and less adaptable, in other parts of the world.'

However, the missive - also signed by Cold War dissidents and renowned conductor Jiri Belohlavek - also acknowledges that 'many Europeans, in the East and in the West, are frustrated with the decreasing ability of the EU to cope with the current problems'.

British playwright Tom Stoppard - who was born in the Czech Republic - was sent the open letter by former ambassador to London Michael Žantovský and has made it public.

Stoppard told the Guardian: 'A lot of the debate in this country is about the arithmetic and it is as well to be reminded that arithmetic isn't everything. Geopolitics in the 21st century weigh more heavily than they ever have done.'

In an interview to coincide with the Eurovision song contest - which Abba won with Waterloo in 1974 - Bjorn said: 'It would really make me sad if Britain would leave and what that would mean. It's like someone you love leaving you. It's emotional.'