The leaked plan, which appeared in the Irish media and has heightened concerns over a return to a hard border, was described as “not quite right” by the prime minister. But in a series of media interviews on Tuesday he would not explain what kind of Brexit plan he would be delivering to Brussels in the coming days, describing it only as “very good”.

Asked on BBC Radio 4’s Today programme if the string of customs checkpoints located five to 10 miles from the border in both Northern Ireland and Ireland was a possibility, Johnson said: “That is not what we are proposing at all.”

He conceded there would ultimately need to be customs checks in some form, adding: “A sovereign united country must have a single customs territory … but there are plenty of ways we can facilitate north-south trade, plenty of ways we can address the problem.”

He said the offer he planned on delivering to the EU was “very good” and would be revealed soon. It was set to include an “all-Ireland” regulation zone.

The prime minister said: “If I may say so, the UK government has already made a very considerable offer and if you look at what we’re saying on the sanitary and phytosanitary arrangements – that is we are already accepting you could have a situation in which, as it were in Northern Ireland, the people are British but the cattle are Irish.

“You have single territory for agriculture, for sanitary and phytosanitary, for agro-foods and that is a big concession by the UK government.”

Should the UK end up with an extension to Brexit as mandated by the so-called Benn Act, he declined to rule out that Britain could use its veto to scupper legislation in Brussels.

Just days ago he had said EU leaders would not want a “truculent and mutinous” UK to remain in the bloc and and they may refuse an extension. The foreign secretary, Dominic Raab, said the UK may not “play nice” if it were locked in with the EU for months on end.

Johnson said: “It’s a matter of common observation, the EU wants us to come out. I don’t think any purpose is served by corralling the UK against its will.

“The EU wants, quite properly, from their own point of view, to proceed with various measures. They want to move towards a defence union, there’s a great deal of pressure to accelerate various projects that we think are not necessarily in the long-term interests of the UK.”

He cited a fiscal union to support the euro as one piece of legislation that could have “considerable consequences in the UK”, which would not be favourably looked upon.

The journalist Charlotte Edwardes’ claim that he groped her thigh during a lunch 20 years ago has overshadowed Johnson’s first Conservative party conference as leader, leading to questions about his behaviour towards women in every media interview he has done at the event.

He told BBC Breakfast said: “I’ve said what I’ve said about that. They are not true. It’s obviously very sad someone should make such allegations.”

As prime minister, he said the nature of his job meant he expected to “come under a certain amount of shot and shell”.

He boasted of how under his tenure as mayor of London, his team had been a “feminocracy” and in his Radio 4 interview he claimed he was still the same “generous-hearted, loving, caring” person he was when he led the capital.

“That person has not gone away. I am a one nation Tory but we are in a position where the only way we can move this country and unite our country again is get Brexit done.”

The Benn Act, the legislation that compels Johnson to ask for an extension for Brexit if he is not able to strike a deal with Brussels by 2019, was described as a “constitutional novelty” by the prime minister.

Controversially describing it again as the “surrender act”, he added fuel to the fire to reports that foreign governments may have been involved in its drafting. “We have no knowledge of how it was produced. It is not subject to normal parliamentary scrutiny. No one knows by whose advice it was drawn up,” he said.

Asked by the Today presenter Nick Robinson about his remarks describing those MPs who worked on the bill as “collaborators”, he said: “I didn’t actually say collaborators. Go back over the quotation, I didn’t say collaborators.”

Robinson interjected: “You said collaboration.”

“Correct,” replied Johnson. “There are different connotations to different words and nobody knows how these bills are produced and with great respect to all my parliamentary colleagues we do need to work out how to scrutinise these things.”

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