The comments came as Downing Street attempts to pile pressure on the EU for swift progress in talks, with just 11 months to complete complex negotiations before Mr Johnson’s self-imposed deadline of December 2020.
The prime minister’s official spokesperson told reporters that the UK would be in a position to begin negotiations on 1 February – the day after Brexit – and pointedly noted that talks could begin with the US first if the EU was not ready.
The prime minister will attempt to inject momentum into the process with a major speech in the days after the formal date of Britain’s departure, setting out his vision of the UK’s place in the world after it leaves the EU.
But in a sign of his desperation to draw a line under the controversy that has divided the country over the past four years, it is understood that he will not utter the word “Brexit” during his address.
The word has already been all but banished from government discourse in the weeks since Mr Johnson won his 12 December election landslide on a promise to “get Brexit done”, even though critics insist that the shape of the UK’s EU withdrawal will not be known until the end of the year.
As news of the prime minister’s planned address emerged, one Whitehall source said: “I wouldn’t expect the word Brexit to be used.”
The speech, in early February, will be followed by the publication of a series of documents formally setting out the UK’s objectives in trade talks with the EU, US and other partners around the world.
EU governments are due to sign off a negotiating mandate for the European Commission to conduct trade talks with the UK at a meeting of the General Affairs Council in Brussels on 25 February, almost a month after Britain ceases to be a member.
But commission spokesperson Eric Mamer has now said that talks with the UK may not start until the following month.
“The commission can adopt its proposal for the negotiation directives only once the UK has actually withdrawn from the EU,” he told a press conference in Brussels.
“But then there is still an institutional process for these to be adopted by the (European) Council. This we know will take some time, which is why we have said we will start negotiations as quickly as we can, but it will certainly not be before the end of February, beginning of March.
“This is not a slowing down or speeding up of the process. This is simply the nature of the institutional process and the consultations that need to take place before the negotiation directives can be formally adopted.”
Any delay in getting talks underway after 31 January will eat into the time available before the end-of-December deadline that Mr Johnson has set for reaching a free trade agreement or allowing the UK to crash out without a deal.
The chief executive of the Best for Britain campaign, Naomi Smith, said: “Boris Johnson is boxing Britain into a corner.
“This latest news that negotiations won’t start until March, coupled with his refusal to extend the transition period, means we are well and truly staring down the barrel of a no-deal Brexit.
“The prime minister must think again, and give the country enough time to secure a relationship with Europe that protects our people, our jobs and our futures.”
Liberal Democrat Brexit spokesperson Alistair Carmichael said: “It has become increasingly obvious that the arbitrary deadline Boris Johnson has set for negotiating the future relationship between the EU and UK is woefully unrealistic.
“With business already in uproar about the Tories’ plans to end pan-European regulatory alignment, the Prime Minister is steering the UK towards some heavy storms.
“People deserve better than a future where a Prime Minister willingly threatens jobs, the environment and the NHS. It is essential that the transition period can be extended to prevent this devastating prospect.”
Mr Johnson’s spokesperson made clear that the UK would not wait for Brussels before opening up talks with other potential trade partners.
“We are ready to begin discussions with countries around the world from 1 February, we are ready to begin discussions with the EU from 1 February,” the spokesperson said.
“The EU have various processes to go through before they are ready to sit down and have their discussions with us.”
He noted that last October’s political declaration between the EU and UK included reference to a “shared intention to conclude agreements giving effect to the future relationship by the end of 2020”.
“That’s what we would expect to be achieved,” said the prime minister’s spokesperson. “They have signed up to this commitment. It’s a formal agreement between the UK and the EU that we should have this process completed by December 2020.”
The spokesperson said that the UK had already undertaken “exploratory” talks with the US on a wide range of issues likely to be included in any trade deal, and that Mr Johnson and Donald Trump had already made clear they wanted a deal to be concluded “as soon as possible”.
On talks with the EU, the spokesperson said: “The prime minister has said repeatedly that we are aiming to negotiate a Canadian-style free trade agreement with no alignment. He set that out directly to the new European Commission president in their first meeting.
“That position is also clearly set out in the manifesto on which the government was elected. When we leave the EU, we will have control of our laws and rules and we will no longer be a rule-taker.
“We are clear on what we want to achieve. You just have to read a single page of the manifesto. The EU is going through a process of working out what its position will be. We are ready to start negotiating on 1 February.”