Remaining in the EU must be an option in a potential second referendum on Brexit, Nicola Sturgeon has insisted.

The First Minister is visiting Westminster calling for an extension to Article 50, which would delay Britain's planned exit from the EU on March 29 next year.

She is pushing for MPs to oppose the Prime Minister's deal and back alternatives like a so-called People's Vote, or a compromise deal where the UK stays in the single market or customs union.

Speaking to STV News, she said it "looks inevitable" Theresa May is going to lose next Tuesday's meaningful vote on the UK Government's Brexit plan.

Sturgeon said: "I'll be interested to hear... what her plan B is, because we need as soon as possible to start talking about the better alternatives to the Prime Minister's deal."

She is meeting May while in London for the second time in recent weeks.

"I don't think I'm sharing any state secrets or breaking any state secrets when I say that these meetings haven't necessarily been the most constructive or productive in the past," the First Minister said.

"What we've seen in the last couple of years is not just a refusal to respect Scotland's distinct interests here, there's been a refusal even to recognise that Scotland has distinct interests."

SNP MPs are set to oppose May's Brexit deal in the crunch Commons vote on December 11, following five days of debate.

Sturgeon said her party's amendment to the UK Government's motion will also call for Article 50 to be extended "to allow time for discussions to be had around the alternatives".

She added: "That discussion I don't think is going to come to a conclusion before the vote on that deal, so it's important we stop the clock ticking in order to allow those discussions to happen afterwards."

The First Minister highlighted her party's preferred option is to remain in the EU - and said if a second Brexit referendum was to occur, it would need to include that option.

Discussions would also need to be had as to whether the "Leave" option in that vote would be for Theresa May's Brexit deal, a no-deal Brexit, or some other form, Sturgeon indicated.

She told STV: "My view is it should be a straightforward choice as to whether the UK wants to stay in the EU, which is my preference, or leave the EU.

"The precise detail of that will, of course, require discussion and ultimately require sanction by the Electoral Commission.

"What I wouldn't countenance is a referendum that didn't have the option of remaining in the EU on the ballot paper.

"So that's my starting point, and that would be the basis on which the SNP would want to have discussions."