Boris Johnson has apologised to Tory members who voted for him to become party leader for not taking Britain out of the EU on 31 October.

The delay was a matter of “deep regret”, the prime minister said, describing extensions as “painful” because they caused the country uncertainty.

Johnson had repeatedly said Brexit would happen at the end of last month, claiming he would rather be “dead in a ditch” than extend the deadline. However, after parliament voted down the timetable for his EU withdrawal bill to be scrutinised, he was forced to request an extension until 31 January.

Asked on Sky’s Sophy Ridge on Sunday programme if he should apologise to Tory members, Johnson said: “Of course, of course. It’s a matter of … it’s a matter of deep regret. But what we need to do now is get on and do it, and the difference between this government and any other party is that only this government offers a deal that is ready to go and a way of delivering it immediately in the middle of December, if we’re lucky enough to get a majority and, of course, it’s a big if and we’ll be working very hard.”

Johnson said the delay was “painful” not for his own ego but because businesses and families could not plan, as they did not know when Brexit was going to be done. He said Labour’s offer of a second referendum would “keep the whole thing going”.

Pressed on whether the public could trust him to keep a promise and deliver on it, he said: “But, don’t forget the circumstances in which that happened. It happened because parliament passed the surrender act.”

Parliament passed the Benn act earlier this autumn, which required Johnson to ask for an extension if he could not get his deal agreed by 19 October.

The prime minister also suggested during the interview that Donald Trump was wrong to say the current withdrawal agreement could harm a UK-US trade deal.

He said: “I don’t wish to cast any aspersions on the president of the United States, but in that respect he is patently in error. Anybody who looks at our deal can see it is a great deal, and what it does is it allows us to take back control of our money, our borders and our laws. But, also, it allows us to have full unfettered control of our tariff schedules.”

On the post-Brexit transition period being extended, he said he could see “no reason whatever” for that to happen as the trade negotiations with the EU “should be extremely simple”.

He said: “We start our negotiations in a state of perfect alignment. We already have zero tariffs and zero quotas.”

He also reiterated his position that the Tories would not strike an election pact with the Brexit party leader, Nigel Farage, who it emerged in the the Sunday Times had twice been offered a peerage by the government. Farage believes this was an attempt to stop him standing his candidates across the country and potentially hitting the Tory vote.

Johnson lost another senior female party member this weekend after the former minister Margot James announced she was standing down as an MP and would not contest the next election.

She follows the culture secretary, Nicky Morgan, the employment minister, Mims Davies, the former minister Claire Perry and the MP Caroline Spelman. The latter cited the abuse she had received over Brexit as her reason for leaving parliament.

James was among the 21 Tory MPs who lost the whip after voting against a no-deal Brexit scenario but had it reinstated last week. The former culture minister and Stourbridge MP told the Stourbridge News there was a “conflict” between her views on the future interests of the country and those of her constituents.

She told the paper: “I was very pleased to receive the whip back and I wanted to continue in parliament. It was only after a period of reflection that I realised that I needed to bring the three-and-a-half-year conflict between the result of the referendum in my constituency and my own view of where the future interests of the country lie to a close.”