British Prime Minister Boris Johnson has said it was a matter of "deep regret" he did not deliver on a promise to leave the European Union on 31 October.

Speaking on the Sky News programme Sophy Ridge on Sunday, Mr Johnson was asked if he was sorry for missing the deadline on Thursday.

"Yes, absolutely," he replied.

When questioned if he would apologise to Conservative Party members who voted for him on the basis he would have sorted Brexit by the end of last month, he said: "Of course, of course. It's a matter of ... it's a matter of deep regret."

Mr Johnson also said he can see "no reason whatsoever" about why the UK should extend the Brexit transition period beyond December 2020, adding: "If you get the right Parliament anything's possible.

"But what you can do from the beginning is, of course, you can begin negotiating, not just with the EU but with countries around the world, and that's one of the great opportunities that we have next year."

Mr Johnson earlier said the UK has secured a "great new deal", saying: "We got Parliament to say it was a good deal, but then they refused to implement it.

"Actually, there was bags of time between that vote to, when they first said it was a good deal and when they could have got us out on October 31."

Told he needed to take responsibility and could not just blame other people, Mr Johnson said: "Well, I do. I do and I'm deeply, deeply disappointed."

Mr Johnson was also asked if he wanted to see a second referendum on Scottish independence.

He told the programme: "I think having another referendum, I don't think people in this country think referendums are very wonderful for harmony."

He added people were told the 2014 vote was a "once-in-a-generation event".

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Meanwhile, the Liberal Democrats are not ruling out a Remain alliance in dozens of seats across the UK for the general election on 12 December.

Also appearing on the Sophy Ridge programme,  Liberal Democrat leader Jo Swinson was asked if the Lib Dems, Plaid Cyrmu and the Greens could work together in up to 60 seats.

Ms Swinson said: "The specifics of announcements will be made in due course but it's well understood that these discussions have been taking place.

"I wouldn't necessarily assume that the numbers are accurate.

"I think it's fair to say that in the vast majority of constituencies the party of Remain that is going to be best-placed to win that seat will be the Liberal Democrats." 

Elsewhere, Nigel Farage has said he will not be standing to be an MP in the general election during an interview on the BBC's Andrew Marr Show.

When asked if he was going to stand in the upcoming election, the Brexit Party leader told Mr Marr: "I've thought very hard about this, how do I serve the cause of Brexit best, because that's what I'm doing this for.

"Not for a career, I don't want to be in politics for the rest of my life.

"Do I find a seat to try get myself into parliament or do I serve the cause better traversing the length and breadth of the United Kingdom supporting 600 candidates, and I've decided the latter course is the right one."

He added: "It's very difficult to do both. It's very difficult to be in a constituency every day and at the same time be out across the United Kingdom." 

The Brexit Party could play a significant role in the election but Mr Johnson has ruled out an election pact.

If the party did stand down hundreds of candidates across the country it would improve the chances of Mr Johnson's Tories gaining a majority or remaining the largest party in a hung parliament.

Mr Farage has said Mr Johnson's Brexit deal is like a piece of cheese.

Speaking to the Sunday Times, he said: "When you get it out of the fridge, it's really appetising and delicious for a few days, but after a couple of weeks it stinks and is inedible."