THERESA May is fearful Nicola Sturgeon will call a new independence referendum to coincide with the start of the formal Brexit process next month, it is being claimed.

According to a London newspaper, the UK Government is preparing for the First Minister to use the triggering of Article 50 in the coming weeks to call a second plebiscite.

Senior UK government told The Times there is serious concern in Whitehall about the prospect with civil servants already under pressure from the Brexit vote and fears over the possible collapse of power-sharing at Stormont.

"It is possible that we will have to face Nicola Sturgeon calling a second referendum, have to bring in direct rule in Northern Ireland and trigger Article 50 all at the same time," an insider said.

There has to be agreement between the UK and Scottish Governments before a referendum can be held.

The 2014 vote was based on the Edinburgh Agreement, signed by then Prime Minister David Cameron and then First Minister Alex Salmond.

The deal allowed for both governments to bring forward a Section 30 order, giving the referendum a legal base.

Both sides agreed that the referendum should take place before the end of 2014 and “meet the highest standards of fairness, transparency and propriety, informed by consultation and independent expert advice”.

May, who heads to Glasgow later this week to address the Scottish Conservatives conference, could reject the First Minister's demand, but such a move is likely to strengthen pro-independence passions.

If she agreed, The Times reported that ministers have been warned, May could risk the break-up the UK on a “coin toss”.

May has promised to trigger Article 50 by the end of March and expects to be able to stick to the timetable, despite ongoing parliamentary wrangling over the process.

The report came as the Prime Minister urged voters in Scotland to use May's council elections to make clear to the First Minister that they do not want to have another independence referendum.

Ever since the UK voted to leave the EU but Scotland voted to stay in, there has been speculation that the Scottish Government will seek to hold another referendum.

Sturgeon has warned that May's plans for a hard Brexit, taking the UK out of the single market, "undoubtedly" made that a more likely prospect.

An SNP spokesman said: "There is already a cast-iron democratic mandate for an independence referendum - that was delivered in last year's Holyrood election, however much the Tories might try to deny it.

"That mandate also stems from the EU referendum, which saw Scotland vote by a 24-point margin to stay in Europe - and Theresa May's reckless pursuit of an economically ruinous hard Brexit will only strengthen opinion in Scotland against leaving Europe.

"The Prime Minister couldn't be more wrong to suggest there is considerable common ground between her Government and the Scottish government on Brexit - her party is hell-bent on taking us out of the world's biggest single market, with all the economic damage that would cause, while we are intent on protecting Scotland's vital national interests."

Downing Street said May remained opposed to a second referendum, although a spokesman refused to be drawn on whether she would block a new vote if Sturgeon decided to call one.

"I'm not getting into hypotheticals," the spokesman said.

The spokesman added: "There was a vote in 2014. The people of Scotland made a decision then to remain in the Union.

"All the evidence around would suggest that Scotland doesn't want another referendum.

"It was a fair, legal and decisive result. Both sides agreed they would abide by the result."

Meanwhile, Scottish Labour has launched a dedicated website TogetherStronger.scot, where people can register their objection to a possible second independence referendum.