Scotland took another step closer to a second referendum on independence after Britain's highest court ruled that the Parliament in Edinburgh has no legal right to challenge Brexit.

Scottish First Minister Nicola Sturgeon, reacting to the ruling, said the British Government's promises to uphold a political convention to consult MPs in Scotland now were "not worth the paper they are written on". She said it's "becoming ever clearer" that Scotland must decide whether it should "take our future into our own hands".

"It is becoming clearer by the day that Scotland's voice is simply not being heard or listened to within the UK," said Sturgeon, leader of the pro-independence Scottish National Party that heads the semi-autonomous Government. "This raises fundamental issues above and beyond that of EU membership."

Prime Minister Theresa May and her Government claim a mandate for Brexit after the UK as a whole voted to leave the European Union in last June's referendum. Yet north of the English border, every region of Scotland voted to stay in the bloc.

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In its ruling, the Supreme Court decided that the UK Parliament will get to vote on triggering the legislation to leave the EU, though there was no legal obligation to do the same in regional legislatures.

While opponents of Brexit welcomed the broader ruling, it means Scotland won't get a say beyond Parliament at Westminster, where the SNP's 54 MPs make it the third-largest party, unable to influence the move toward the EU exit.

That impotence reinforces the nationalist argument that the political system in the UK can't accommodate Scotland, according to Nicola McEwen, associate director at the Centre on Constitutional Change at Edinburgh University.

"It places the focus where it's always been and if it doesn't lead to any consensus it will make another independence referendum highly likely," said McEwen.

With each twist and turn in the Brexit debate that's convulsing Britain, another vote on Scotland breaking away from the rest of the UK appears more imminent.

Polls currently suggest the result would mirror that of a referendum in 2014, when Scots voted 55 per cent to 45 per cent against independence, but Sturgeon can now lay claim to an argument with which to sway sceptics: that Scotland is being side-lined democratically.

After ordering her ministers to prepare legislation for another independence referendum, Sturgeon put forward a package of proposals in December to keep Scotland's access to the single market and free movement of people. She called it a compromise and May said she would listen.

Then last week, May outlined a vision for Brexit that involved leaving the single market and potentially walking away from the EU without a deal. Sturgeon said the UK Government thinks it "can do anything to Scotland and get away with it".

The Scottish Government has to be seen to be doing everything it can to compromise and cooperate, said McEwen. There's no sign at the moment that the British Government is willing to accommodate Scotland's wishes, she said.

Given the current polling, "the Scottish Government doesn't want to risk pushing ahead with a referendum on independence," McEwen said. "'But if they have to do it, they'd want to show they've exhausted all other possibilities so they can say it's a democratic issue."