By Elisabeth O'Leary
ABERDEEN, Scotland (Reuters) - A continued refusal by Britain's prime minister to discuss an independence referendum authorized by the Scottish parliament would "shatter beyond repair" the United Kingdom's constitutional structure, Nicola Sturgeon will tell the Scottish National Party on Saturday.
Sturgeon will press on with plans to hold a new Scottish independence referendum as announced earlier this week, and expects to get authorization from the devolved parliament on Wednesday to seek a new vote once the terms for Brexit are clear but before Britain leaves the EU.
But Prime Minister Theresa May needs to sign off on any legally binding vote in Scotland under the UK's constitutional arrangements, and she told Sturgeon this week that "now is not the time" for a new choice on independence. [L5N1GT4LN]
"To stand in defiance of (Scottish parliamentary authorization) would be for the Prime Minister to shatter beyond repair any notion of the UK as a respectful partnership of equals," Sturgeon, who is also Scotland's First Minister, will say.
"She has time to think again and I hope she does. If her concern is timing then -- within reason -- I am happy to have that discussion," Sturgeon will say.
The two sides are in a standoff just days before Britain is expected to trigger Article 50 of the EU's Lisbon Treaty and start the extremely complicated divorce procedure.
Last June's vote to leave the EU has altered the political landscape and shaken the ties of the United Kingdom's four nations. England, the UK's most populous nation, and Wales voted to leave while the Scots and the Northern Irish wanted to keep their EU membership.
While Sturgeon, who leads the devolved government, told Scottish television on Friday that she still has "options" if May refuses to acknowledge her mandate to call for a new secession vote, she declined to say what those options were.
There has been talk by delegates at the conference of the possibility of a consultative referendum, that is, a poll not authorized by the British parliament.
"This is a step by step process. If we send an envelope to May and she returns it unopened, then we have the UK government not talking to the Scottish government," said a senior SNP source. "That is a constitutional crisis, or something very close to it," the source said.
Scottish voters rejected independence in 2014 by a 10 percentage point margin, and the issue of secession is still hotly contested. But Sturgeon was elected last year on a manifesto which included the possibility of a new independence vote if there were a material change in circumstances "such as Scotland being taken out of the EU against our will."
"We can still decide which path we take," Sturgeon will say. "Whatever our different opinions on independence, we can all unite around this simple principle: Scotland's future must be Scotland's choice."
Speaking separately in Scotland, former prime minister Gordon Brown -- who still has sway with many Scots who want to keep ties to the UK -- said Brexit had torn up the status quo and there was a need for new powers for the devolved Scottish parliament.
"The third option, a patriotic Scottish way and free from the absolutism of the SNP and the do-nothing-ism of the (Conservatives) is now essential because post-Brexit realities makes the status quo redundant and requires us to break with the past," Brown, of the Labour Party, told a Festival Of Ideas in Kirkcaldy.
(Reporting by Elisabeth O'Leary; Editing by Hugh Lawson)