LEGAL action to clear a path for a Scottish independence referendum could be launched by a member of the public, a constitutional expert has claimed.

Nicola Sturgeon has pledged to fight the Prime Minister's decision to delay a second vote with her insistence that ''now is not the time".

Answering questions during a visit to California’s Stanford University, the First Minister has hinted at possible legal action to hold a plebiscite.

She said that Mrs May’s government “must recognise that the people of Scotland have the right to make (the) choice” on independence.

And added: “One of the things reserved to the UK government is the constitution.

“It is quite a vague term. It’s never been tested in court but in 2014 we accepted that for there to be a referendum in Scotland it required the legal consent of the UK government.”

Opposition politicians accused her of looking for backing from the courts because she had lost the support of the public.

But experts said that Ms Sturgeon was right.

Alison L. Young, professor of public law at Hertford College, Oxford, who has written on the issue with her colleague Ewan Smith, said: “The First Minister is right to say that is not necessarily clear cut, there has not been a legal case on this. So it is possible that if things progress there may be a legal case raised which would have to resolve this issue.”

Legal action was not an option limited to Scottish ministers, she added, with the potential for a case to be crowdfunded by individuals.

Conversely, should the Scottish Parliament legislate to accelerate a referendum Mrs May's government may have to decide whether it too should fight it in the courts, she suggested.

Earlier this year Gina Miller, a British businesswoman, successfully challenged Mrs May's right to serve divorce papers on the EU without a vote by MPs in the Supreme Court.

Ms Sturgeon has said that if Mrs May continues to reject her call for an agreement on another referendum she will return to Holyrood after Easter “to set out the steps that the Scottish Government will take to progress this Parliament’s will”.

Professor Nick Barber, also from Oxford University and an expert in constitutional law, told Buzzfeed that he would "take the view that the Scottish government could hold an advisory referendum on independence.

"Matters related to the Union are reserved, but whilst the Scottish parliament and government lack the power to make decisions within reserved areas it does not follow they lack the power to form opinions on these matters or to negotiate on these issues with Westminster.

"An advisory referendum on a reserved issue would be a way in which the Scottish institutions could demonstrate the strength of feeling in Scotland on the issue, and could play a part in that negotiation process."

Scottish Lib Dem leader Willie Rennie said: “The First Minister is seeking support of the courts as she has lost the support of the public.

“Wasting taxpayers money on a court case in pursuit of Nicola Sturgeon’s independence obsession will infuriate patients who are waiting for treatment and parents who want a decent education system."

It is understood the Scottish Government is not currently pursuing the idea of a court challenge.

A spokesman for the First Minister said that there was a "cast-iron" democratic mandate for a vote.

“We agree with the Prime Minister that now is not the time for a vote, but if the UK Government’s intention is to try and indefinitely block a referendum that would be utterly undemocratic and unsustainable," he said.

“People across Scotland already disagree with that stance, and public opinion is only likely to turn even more sharply against the PM the longer she tries to stick to that position.”

While in the US Ms Sturgeon also reiterated her stance that she would be willing to meet controversial American President Donald Trump if he comes to Scotland when he visits the UK later this year.