THERESA May is running out of excuses to refuse a second referendum, Nicola Sturgeon said last night, after the Prime Minister claimed Brexit would be wrapped up in 24 months.

Speaking after they met in Glasgow, the First Minister said Mrs May told her details of both the Brexit divorce and the UK’s future trading deal with the EU would be clear by spring 2019.

Ms Sturgeon, who has called for a referendum between autumn 2018 and spring 2019, seized on Mrs May’s bullish timetable and said it dovetailed neatly with her own, enabling voters to make an informed choice between Brexit in the UK and independence.

She said: “I think it makes it very difficult for the Prime Minister to maintain a rational opposition to a referendum in the timescale I have set out. I think she has got a perfectly rational opposition to a referendum now, which is why I am not proposing it.

"But based on the discussion today, I would struggle to see what her rational opposition to it would be in the timescale we have been talking about."

Mrs May has ruled out a referendum before Brexit is finalised, saying “now is not the time” for a constitutional fight that would distract from two years of complex negotiations with Brussels.

However the Prime Minister, who is due to invoke the Article 50 withdrawal process from Europe tomorrow, has not ruled out a ballot indefinitely.

HeraldScotland:

Mrs May repeated her “now is not the time” mantra on a visit to Scotland yesterday.

She said: ''My position is very simple and it hasn't changed. It is that now is not the time to be talking about a second independence referendum and that's for a couple of reasons.

''First of all, now is the point when we are triggering Article 50, we're starting negotiations for leaving the European Union. Now is the time when we should be pulling together, not hanging apart. Pulling together to make sure we get the best possible deal for the whole of the UK.

'It would be unfair on the people of Scotland to ask them to make a significant decision until all the facts were known, at a point where nobody knows what the situation is going to be."

She said she wanted to build a ''more united nation'' as Britain leaves the EU.

But speaking to the media after meeting Mrs May at a Clydeside hotel, the First Minister used the Prime Minister’s own timetable to advance her claim to a referendum.

She said: “She [Mrs May] is absolutely adamant that she believes the terms of Brexit, by which she means both the exit terms, the divorce deal, and the detail of a comprehensive free trade agreement - in other words the future relationship between the UK and the EU - will be clear before the UK exits the EU.

“When I put it to her that what she was suggesting was that in a period of around 18 months from now to two years from now the terms of the future relationship between the UK and the EU would be clear, she said, ‘Yes’, that is what she was saying.

“Obviously that is relevant around the terms of an independence referendum.”

Ms Sturgeon she had been “at pains” to understand Mrs May and checked she meant the terms of Brexit would be known around autumn 2018, before the six-month ratification round by the other 27 EU states ahead of Brexit in March 2019.

She said: “If you say now is now the time then you are implicitly accepting there is a time.

“The reason for ‘now not being the time’ is that the terms of Brexit are not clear.

“Therefore if she [Mrs May] is saying that she believes the terms of Brexit will be clear before exit and in time for EU ratification, then it seems to me that she therefore has no basis for standing in the way of that timescale.”

She said the meeting had been “pretty cordial” and “businesslike”, but there was no guarantee on returning powers repatriated from Brussels to Holyrood after Brexit.

She reminded the Prime Minister that MSPs vote today on whether to request a Section 30 order to transfer referendum powers to Holyrood.

Mrs May has already said she will rebuff the request.

Ms Sturgeon said she would be in touch with the UK Government “later this week” on the back of the vote, which is expected to pass easily with the support of SNP and Green MSPs.

Tory sources described the meeting as "courteous” but described the First Minister as "obsessed with process”.

One said: “She’s trying to suggest there has been a breakthrough when in reality what we have is the confirmation of a date. We all know the timetable - it is Wednesday and two years from Wednesday we will be out of the EU. It is not about the activation of the deal, it is about seeing it work in practice and letting the whole Brexit process play out.”

In private, some Tories admit they hope to push a referendum beyond the 2021 Holyrood election, in the hope the SNP loses ground and a referendum becomes impossible.

A No 10 source last night raised another possible obstacle in the form of “phased implementation” of some areas of Brexit.

The source said: "We have always been clear that people would need to know what they are voting on. Clearly that requires people to be aware of the operational realities of Brexit, not just the outlines of a draft deal 18 months in."

A Scottish Government insider said if Westminster repeatedly offered excuses for not holding a referendum its position would be “unsustainable”.

Scottish Tory MSP Murdo Fraser said: “Nicola Sturgeon has once again failed to act today as a First Minister for all of Scotland.

“We are just about to enter the most important international negotiations this country has taken part in for decades, and all the First Minister can think about is raising a timetable for a referendum that most people in Scotland don't want.

“The SNP has shown that it is interested only in process rather than substance.

“Nicola Sturgeon has made it clear she no longer wants to govern for everyone in Scotland, she just wants to use meetings with the Prime Minister to further her campaign for separation.”