By Elisabeth O'Leary

EDINBURGH (Reuters) - Scotland will throw its weight behind campaigners trying to force the British government to seek parliamentary approval to start the formal divorce procedure from the European Union, First Minister Nicola Sturgeon said on Tuesday.

Although the United Kingdom as a whole voted to leave the EU in a June referendum, Scotland voted to remain and Sturgeon has vowed to protect Scottish interests in the coming negotiations with Brussels.

British Prime Minister Theresa May has said she will begin the exit from the EU by triggering Article 50 of the EU Lisbon Treaty before the end of next March and argues she can do so without the approval of parliament.

But a legal case coming before the Supreme Court next month challenges her right to start the process without a green light from lawmakers, and Scotland will side with those opposing her, Sturgeon said.

Scotland's most senior legal officer, the Lord Advocate, will lodge a formal application at the Supreme Court requesting to intervene in the case.

"Triggering Article 50 will directly affect devolved interests and rights in Scotland and deprive Scotland of rights and freedom," Sturgeon told reporters.

"I recognize and respect the rights of England and Wales to leave the European Union and this is not an attempt to veto that process, but the democratic wishes of people in Scotland ... cannot simply be brushed aside," she said.

Sturgeon, a nationalist who heads the devolved Scottish government, said she believes that if courts decide definitively that the process of leaving the EU needs an act of parliament, Scotland's devolved parliament should also be formally consulted.

That could slow the Brexit process down further.

Sturgeon argues independence should continue to be an option for Scotland, although there is no evidence that support for it has changed since nationalists lost a referendum by 10 percentage points in 2014.

She says May's government has no mandate to take any part of Britain out of the single EU market for goods and services, and has been pushing for more access to and influence on the British government's strategy.

But said she had no more clues on what path Britain wanted to take than she had after a "frustrating" meeting with officials in London two weeks ago.

"(Carmaker) Nissan has a clearer indication of strategy than the elected governments of Wales, Scotland and Ireland," she said.

The British government said last month it had given Nissan assurances that its new investment in plant in Britain would remain competitive after Brexit but has declined to go into details of the agreement.

(Editing by Stephen Addison)