The Foreign Secretary is alleged to have urged the Germans to turn Brexit into an economic opportunity during un-minuted discussions in Berlin.
Mr Johnson is understood to have been referring to the continual and complicated Brexit negotiations rather than the vote to leave the EU overall, as he campaigned for the decision in the referendum.
Sources in Brussels say the MP for Uxbridge and South Ruislip was rebuffed by the German government, which has repeatedly stood behind European Union chief Brexit negotiator Michel Barnier and resisted any attempts to go over his head.
The meeting is assumed to have taken place during his November 2016 visit to Berlin or a separate visit in April last year.
The claims have been vehemently denied by his friends, who claimed they were a smear and hatchet job, on Tuesday evening.
One friend of Mr Johnson said: “These old claims will be rightly dismissed as nonsense by anyone sensible. Boris knows Brexit will be a great success and is committed to taking back control of our money, laws and borders.”
On Tuesday, EU diplomats said informal talks had begun of European Union governments demanding the continued free movement of their workers to Britain, after Brexit, as a trade for giving British bankers access to the single market.
They suggested the idea had been floating in Brussels; corridors of power awaiting talks over the future UK-EU relationship and free trade agreement.
The plan came to light after Secretary of State for Exiting the European Union David Davis called for a system of mutual recognition of standards, which would allow market access on both sides, post-Brexit.
At a speech in Vienna, Mr Davis insisted Brexit would not lead to an Anglo-Saxon bonfire of regulations or create a “Mad Max” dystopia.
The commission is currently sticking to the hard line stance that financial services will lose their passport to the single market after 2021’s Brexit transition period.
Brussels also insists freedom of movement must be upheld until the transition period ends.
A senior EU has suggested any significant deal on financial services is likely to be conditional on a significant form of free movement and include those in lower-paid jobs than banking.
While bankers and the City of London are keen to maintain the status quo, Theresa May would face increased criticism should she compromise Britain’s borders in an exchange.
The EU-27 (or, EU countries sans Britain) demands are expected to come in negotiations over the contentious free trade deal or the treaty governing the UK’s future relationship with the EU.
One EU diplomat said: “If the UK wants a bespoke deal including financial services we need different bespoke redlines. And in that scenario, of course, the question ‘what’s in it for us’ will be asked.”
Another diplomat added: “In line with the EU-27 thinking, being in the single market means respecting all its four freedoms, not just one of them.”