Johnson and Cameron at odds over EU business backing
Boris Johnson has accused David Cameron of a "stitch-up" over the role played by business in the EU referendum.
He said a letter from the boss of Serco to David Cameron suggested "collusion" between business and Downing Street.
The letter mentioned how support for EU membership could be "mobilised" - and also discussed further privatisation of the prison estate.
Mr Cameron, meanwhile, has suggested the head of so-called Islamic State may be pleased with a vote to Leave.
Speaking in London, the prime minister said Abu Bakr al-Baghdadi, the leader of so-called Islamic State in Iraq, "might be happy" in the event of a Leave vote in June, remarks which Mr Johnson said were a "bit too much".
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Vote Leave has seized upon a leaked letter, published in the Daily Mail, from Rupert Soames - the head of the outsourcing firm Serco - to the prime minister on 8 February, in which he refers to a meeting with Mr Cameron the week before.
Mr Soames, whose brother is the pro-EU Tory MP Nicholas Soames, wrote he was working with Lord Rose - chair of the Britain Stronger in Europe campaign group - and Lord Chadlington, a long-term ally of Mr Cameron's - with a view to contacting some of the UK's largest firms to persuade them to highlight the perceived risks of leaving the EU in annual reports released before the 23 June poll.
"Thank you for a very useful meeting last week," he wrote. "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... All public companies are required to set out in their Annual Report an analysis 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."
'Do down Britain'
In his letter, Mr Soames also raised the issues of prison reform and the case for greater private sector involvement in the running of prisons. Serco currently operates six adult prisons in the UK and one juvenile training centre.
The letter was written on the same day Mr Cameron made a speech promising the "biggest shake-up of prisons since the Victorian era", including piloting six "reform prisons" to tackle high levels of violence and re-offending.
Vote Leave said the letter showed Downing Street "had been doing deals with businesses to exaggerate the risk of a vote to leave the EU".
Mr Johnson, the former mayor of London who is now a leading Tory Leave campaigner, said it showed the PM's efforts to renegotiate the EU's membership had been the "biggest stitch-up since the Bayeux Tapestry".
"Everybody is allowed to make their point but it is important that we look at what is really going on," he said on a trip to Stafford.
"When you have what looks like collusion between Downing Street and big Remain-supporting businesses. On the surface, it seems to be suggesting that in exchange for support to remain, there is consideration to be given to the exchanging of lavish public sector contracts.
"I think we need to a full explanation of what is going on without delay."
Britain Stronger in Europe said Mr Johnson was "shouting out conspiracy theories" when he had been a strong supporter of Serco while he was in charge of London. It accused him of "stunning hypocrisy" over outsourcing and other EU-related issues.
Both No 10 and Serco said they would not comment on the details of a leaked letter. The company, which had a turnover of £3.5bn last year and more than £100m in contracts with EU institutions, has said before that leaving the EU would be a risk to its business.
Speaking to business leaders in London, Mr Cameron said they should "feel free" to speak out on either side of the argument and not be cowed by the politicised nature of the debate.
"The British public deserve to hear from business, large and small, about what they think," he said. "I don't want anyone to wake up on 24 June and feel they were not given the facts and the figures."
The Leave campaign, he suggested, was "losing the argument" and there was a "clear consensus" that quitting the EU would be damaging for both the economy and security.
Meanwhile, the CBI has mobilised dozens of businesses to write to employees explaining why they want to remain ahead of the 23 June poll.
Carolyn Fairbairn, the organisation's director general, said the move was "not about telling people how to vote" but rather an effort by "responsible business leaders" to explain to staff the effect Brexit would have on their companies and their livelihoods.
Former British Chambers of Commerce boss John Longworth said the CBI's involvement was an "anti democratic abuse of power" from an organisation which "supported the ERM and the single currency".
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