EDINBURGH • Scotland will start preparing for an independence referendum before May 2021 without permission from London, First Minister Nicola Sturgeon has said.

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," Ms Sturgeon told Scotland's devolved Parliament on Wednesday.

She said a devolved Parliament Bill would be drawn up before the end of this year and that Scotland, which has 8 per cent 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 UK voted to leave the EU in a 2016 referendum with a 52-48 per cent margin, but while Wales and England voted 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 UK.

The Scottish National Party, 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 with Brexit, Ms Sturgeon is under pressure from independence supporters to offer a clear way forward in the quest to break from the UK.

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

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

REUTERS