Theresa May has admitted she must secure her Brexit deal in just 18 months, the SNP has said - claiming it clears the way for a second independence referendum within two years

Nicola Sturgeon leapt on the comment to argue there was now no "rational" argument against the poll, because Scottish voters would be able to make an informed decision as the Prime Minister has demanded.

Ms May has insisted the poll cannot be held within two years because the Scottish people would not know the outcome of the Brexit talks.

But Mike Russell, the SNP’s Minister for UK Negotiations on Scotland’s Place in Europe, said: “The Prime Minister has confirmed to the First Minister that the timescale is 18 months for negotiations to get the framework to make sure there’s something to be voted up on by the European Parliament.

“In other words, she expects this deal to be done within the 18 month period, with six months for ratification.

“That is the timescale we have indicated in our resolution, so there is an agreement on the moment at which enough will be known for the people of Scotland to make an informed decision.”

Ms Sturgeon added: “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.”

The Prime Minister has never publicly acknowledged what some EU leaders have put forward as the inevitable shortened timetable for the Brexit negotiations.

Article 50 says the exit talks can run for two years, but six months will be required for the European Parliament to ratify any deal, it is argued by Brussels.

No.10 was caught by surprise when Michel Barnier, the European Commission’s lead Brexit negotiator, laid out the 18-month timetable in December – refusing to confirm it.

There was no immediate official comment from Downing Street on the face-to-face talks, which took place in a Glasgow hotel room.

However, a Government source insisted its position on Brexit – and a Scottish referendum – had not changed, that a deal would take a “minimum of 18 months and a maximum of 24 months”.

“We still think this is the wrong time to have a discussion about a referendum,” the source said. “Eighteen months is not enough time to give people an informed choice about what the options are.”

The crunch talks were the first face-to-face meeting between the two leaders since Ms May blocked Scotland’s bid for a second independence referendum.

They were staged just one day before the Edinburgh Parliament is due to vote on issuing its formal demand for a poll aimed at breaking up the 300-year Union.

In order to hold a legally-binding poll, Edinburgh must be granted an ‘Order in Council’ by Westminster under Section 30 of the 1998 Scotland Act.

Earlier, Ms May insisted she would not bending under SNP pressure, saying: “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.

“Also I think 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.”

The Prime Minister rejected SNP protests that her Government had refused to explain the role the Scottish Government will play in the Brexit negotiations, or how its interests will be represented.