Video report by ITV News Correspondent Peter Smith

Nicola Sturgeon has insisted she will plough ahead with plans for a second Scottish independence referendum - despite the Prime Minister rejecting her call.

If Westminster does not back her, she warned, there are "options" for the Scottish government to act.

It comes after Theresa May repeatedly said "now is not the time" to be discussing the division of the union, warning it threatened to undermine the UK's Brexit negotiations.

Speaking to ITV News Scotland correspondent Peter Smith at the SNP conference in Aberdeen, the Scottish First Minister said she agreed "now" was not the time.

But, she said, the wheels needed to be put into motion now if such a referendum were to be held in autumn next year as set out in her plan.

I agree with Theresa May that now is not the time for a referendum. Nicola Sturgeon

She said she had not plucked the timescale "out of nowhere", but was basing her plan for another referendum in autumn 2018 on the Prime Minister's own schedule.

If Article 50 is triggered this month as anticipated, that would see the UK leave the EU in March 2019.

Ms Sturgeon said if the UK is to agree a deal with the EU before that point, it would mean the terms of the deal would need to be known by autumn 2018 in order to be ratified in time.

"That - not before that - would be the point at which to give the people of Scotland a choice - before it's too late for Scotland to choose a different course," she said.

"If we don't indicate to Europe either before the UK leaves or fairly shortly after that that we want a different relationship to the one with the rest of the UK then we make it much more difficult for Scotland to negotiate a different path forward."

She said the plan she had set out was "common sense, fair and reasonable", and challenged Ms May to set out when she believes a referendum would be appropriate, if she disagrees with next autumn.

If she refuses to discuss the matter at all, she said, "then she's seeking to block the choice of the Scottish people and that is unacceptable".

She refused to discuss what her 'Plan B' might be if Westminster continues to refuse to discuss a second referendum, even after a vote on Wednesday which is expected to see the Scottish Parliament approve Ms Sturgeon's proposals.

She said she would consider "various options", but declined to reveal what they might be, insisting that the "democratic ground" of her position was stronger than Ms May's.

I think the pressure should still be on the Prime Minister to realise what an unsustainable position she's in, before people start asking me what 'Plan B's are. Nicola Sturgeon

Meanwhlie, at the Conservative Spring Forum in Cardiff, Theresa May said it was vital for the UK to "pull together as one".

She said she would "always fight to strengthen and sustain this precious, precious union" - and hit out at the "divisive and obsessive nationalism" of both the SNP and Plaid Cymru.