The London Mayor put the case for Brexit in effusive terms, calling the referendum scheduled for the 23 June a “once in a lifetime opportunity that will not come again”.
Mr Johnson said he had experienced first-hand how EU directives impacted Britain, saying it took UK officials a year to convince Brussels that the Crossrail project didn’t need 50 per cent wider tunnels to accommodate German trains.
And hitting out at what he described as the negative tactics of the Remain campaign, he said: “This is like the jailer has accidentally left the door of the jail open and people can see the sunlit land beyond.
“And everybody is suddenly wrangling about the terrors of the world outside. Actually it would be wonderful. It would be a huge weight lifted from British business.”
Mr Johnson spoke at length about Britain’s “proud democracy” and the need to “take back control over our borders and control over our democracy”.
But in an at-times acrimonious interview, the Tory MP struggled to focus in on the specifics of what leaving the EU would mean for the UK.
Mr Marr asked repeatedly if Mr Johnson was still in favour of the idea of the single market – as he has said before – and whether he wanted Britain to still be part of it outside the EU.
And Mr Johnson also refused to be pinned down on exactly who he was accusing when he said business leader John Longworth had paid a “heavy price” for expressing his support for Brexit.
What has the EU ever done for us?
What has the EU ever done for us?
1/7 1. It gives you freedom to live, work and retire anywhere in Europe
As a member of the EU, UK citizens benefit from freedom of movement across the continent. Considered one of the so-called four pillars of the European Union, this freedom allows all EU citizens to live, work and travel in other member states.
2/7 2. It sustains millions of jobs
A report by the Centre for Economics and Business Research, released in October 2015, suggested 3.1 million British jobs were linked to the UK’s exports to the EU.
3/7 3. Your holiday is much easier - and safer
Freedom to travel is one of the most exercised benefits of EU membership, with Britons having made 31 million visits to the EU in 2014 alone. But a lot of the benefits of being an EU citizen are either taken for granted or go unnoticed.
4/7 4. It means you're less likely to get ripped off
Consumer protection is a key benefit of the EU’s single market, and ensures members of the British public receive equal consumer rights when shopping anywhere in Europe.
5/7 5. It offers greater protection from terrorists, paedophiles, people traffickers and cyber-crime
Another example of a lesser-known advantage of EU membership is the benefit of cross-country coordination and cooperation in the fight against crime.
6/7 6. Our businesses depend on it
According to 71% of all members of the Confederation of British Influence (CBI), and 67 per cent of small and medium-sized enterprises (SMEs), the EU has had an overall positive impact on their business.
7/7 7. We have greater influence
Robin Niblett, Director of think-tank Chatham House, stated in a report published last year: “For a mid-sized country like the UK, which will never again be economically dominant either globally or regionally, and whose diplomatic and military resources are declining in relative terms, being a major player in a strong regional institution can offer a critical lever for international influence.
Asked about the way he came out in favour of leaving the EU, Mr Johnson said he was involved a process of seeking a new wording of the clause that would return sovereignty to the UK.
He said that the Government’s lawyers “exploded” the entire document, saying it could never work with EU treaties – and confirmed that was the moment he decided to support Out.
That may well anger David Cameron and the Cabinet, who were led to believe Mr Johnson made a last-minute decision on Sunday evening two weeks ago after hearing the Prime Minister speak himself on the Andrew Marr Show. Downing Street has previously criticised the way the Mayor conducted the announcement.
Meanwhile, asked if he expected to become the next Prime Minister, Mr Johnson briefly obfuscated before giving his clearest answer of the entire morning.
“Certainly not,” he said. “We have a wonderful Prime Minister, and to the best of my knowledge there is not a single European leader who has had to step down because of a referendum, on Europe or not.
"The whole thing is cobblers, you are just trying to personalise it to make it more interesting for viewers,” he added.