The SNP is “absolutely united” on its approach to Brexit, Ian Blackford, its Westminster leader, has insisted despite one senior backbencher publicly breaking ranks to oppose the party’s support for a pre-Christmas election.

Angus Brendan MacNeil denounced his party leadership’s support for a December 9 poll, claiming that when the proposition was made "jaws were on the floor" among parliamentary colleagues.

The MP for Na h-Eileanan an Iar tweeted: "I am not getting bounced into this..Thursday it was 'madness' to have a winter election. Any election now will be a Proxy Brexit referendum and Hard Brexit could be won in 6 weeks on only 35% to 40% of the vote!!"

He admitted he was “at odds with my own party,” asserting that Parliament should “not be giving the PM the Christmas present he wants”.

Mr MacNeil declared: “We should keep Boris Johnson in his cage” and warned about the aftermath of a Christmas election, which he suggested could give the PM a mandate for “any Brexit” and face the country with five years of a Johnson “super-majority”.

Last night, the Western Isles MP told Sky News the PM was a “vulture in a cage,” and the SNP should keep him there to “emasculate him”.

Earlier, Mr Blackford was asked what sanction there would be for any SNP MP who defied the party whip in today’s vote on a pre-Christmas election but declined to answer, saying the proposition was “hypothetical”.

He also refused to say if he had had a conversation with Mr MacNeil, saying he would not discuss “what we will do on an internal basis,” but he stressed that he had had talks with colleagues at Westminster and the party was “absolutely united in what we should be doing”.

Asked how he could profess unity given Mr MacNeil’s outburst, the Highland MP replied: “There is a unity of purpose in this party that we want to fight an election…on Scotland’s right to choose and I would expect every colleague to get behind that.”

The leadership’s attitude towards a December poll also appears to have changed. Last week, Mr Blackford suggested the PM’s intention to hold one was “barking mad,” noting: "People are not going to thank you for asking them to come out and vote in a General Election when we're in the middle of winter."

But the party leader stressed how the window was closing on an election and he wanted to see it happen as soon as possible.

"Of course, there are challenges in having an election in winter. I don’t think when it comes to the public it’s that much of an issue because our experience is the public will come out; it’s more of a challenge for us to get out and speak to the electorate because of the restricted daylight hours but that’s life and it’s something you have to accept and get on with.”

Asked if he had not performed a remarkable flip-flop in the space of 24 hours, Mr Blackford replied: “I was reflecting on Boris Johnson trying to deliver an election having taken us out of the EU and doing that close to Christmas. We have got to accept our responsibilities and an election is the only way we can get out of this and the reason for coming together with the Liberals on the one-line bill is to try and do that.”

Emphasising how 19 Labour rebels would continue to support the Government’s Withdrawal Bill, he declared: “Doing nothing will deliver Brexit. We’re saying put this back to the people so they can reflect on where we are. We don’t want Brexit to happen; period.”

Mr Blackford added: “The ultimate sanction we have is to have our own referendum on independence in 2020 and that’s what the basis of the election campaign will be fought on. It will be reinforcing the mandate that we have that we won in 2016 Scottish elections…In a sense, we have an insurance policy and that is the right of the people of Scotland being able to choose their own destiny.”

Meanwhile, the mood among Scottish Conservative MPs against a December election also appears to have changed.

During the Tory conference in October, a number of Tory MPs representing rural Scottish constituencies complained about the prospect of a late autumn poll in the run-up to Christmas; indeed, they had personally lobbied Mr Johnson against it.

But last night one senior backbencher explained: “The public mood has changed. Voters have moved on and want to end the Brexit gridlock. We’re now all ready for an election before Christmas.”