EDINBURGH (Reuters) - Scotland will start preparing for an independence referendum before May 2021 without permission from London, First Minister Nicola Sturgeon said on Wednesday.

Scotland's First Minister Nicola Sturgeon speaks in the Scottish Parliament during continued Brexit uncertainty in Edinburgh, Scotland, Britain, April 24, 2019. REUTERS/Russell Cheyne

Scotland, England’s political partner for more than 300 years and part of the United Kingdom, rejected independence by 10 percentage points in a 2014 referendum. But differences over Brexit have strained relations with the government in London.

“A choice between Brexit and a future for Scotland as an independent European nation should be offered in the lifetime of this parliament,” Sturgeon told Scotland’s devolved parliament.

She said a devolved parliament bill would be drawn up before the end of 2019 and that Scotland, which has 8 percent of Britain’s electorate, did not need permission at this stage from London.

London’s approval, however, would eventually be necessary “to put beyond doubt or challenge our ability to apply the bill to an independence referendum,” she said.

The United Kingdom voted 52-48 to leave the EU in a 2016 referendum, but while Wales and England vote to leave, Scotland and Northern Ireland voted to stay.

In the campaign for the 2014 independence referendum, unionists said that the only way for Scotland to stay in the EU was to stick with the United Kingdom. The Scottish National Party (SNP), which runs the devolved government in Edinburgh, says that a second referendum is justified as Scotland is now being dragged out of the bloc against its will.

With most Scots unhappy at Brexit, Sturgeon is under pressure from independence supporters to offer a clear way forward in the quest to break from the United Kingdom.

Britain is mired in political chaos and it is still unclear whether, when or even if it will leave the European Union.

John Curtice, professor of politics at Strathclyde University and Britain’s leading polling expert, said Sturgeon was keeping her own troops happy while leaving her options open.

She probably has until October or November of 2020 to hold a new vote once Brexit happens, he said.

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Since Scots rejected independence 55-45 percent in 2014, polls show that support has changed little. Grassroots supporters will launch a new campaign this week before the SNP spring conference this weekend.

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“I think she was implicitly acknowledging that while it might be impossible (to get permission) out of the current (UK) parliament, it might be a lot easier if we get a general election between now and the end of the year, and the SNP may well find itself in the kingmaker role,” Curtice told Reuters.

Her address took a noticeably conciliatory tone.

“The question that confronts us now is this: if the status quo is not fit for purpose - and I know even some of the most committed believers in the union find it hard to argue that it is - how do we fix it?” she said.

Those who want to maintain the United Kingdom argue that Brexit has made no difference to how Scots feel, and the secession vote should not be repeated.

“Nicola Sturgeon continues to press for divisive constitutional change when it is clear that most people in Scotland do not want another independence referendum,” said David Mundell, Britain’s Scotland minister.

Sturgeon argued that leaving the world’s largest trading bloc endangers Britain and Scotland’s economic well-being.

“We face being forced to the margins, sidelined within a UK that is itself increasingly sidelined on the international stage. Independence by contrast would allow us to protect our place in Europe.”