Image copyright Getty Images Image caption Alex Neil is a former health secretary in the Scottish government

An SNP victory in the next Scottish Parliament election could give the party a "mandate for independence", one of the party's senior MSPs has claimed.

Alex Neil said winning the election in 2021 would potentially allow the SNP to begin independence negotiations.

But he stressed this would only be the case if the UK government continued to refuse consent for a referendum.

SNP leader Nicola Sturgeon says a legal referendum is the only way for Scotland to win independence.

She wants to hold one next year - but the UK government has already said it would refuse to grant a Section 30 order, which provided the legal basis for the 2014 independence referendum.

Some activists and elected representatives within the SNP and wider independence movement believe Ms Sturgeon is being too cautious, and have called on her to set out a so-called Plan B.

They include SNP MP Angus MacNeil and Inverclyde councillor Chris McEleny, who have argued that the party winning a majority of Scottish seats in an election would be enough for independence negotiations to begin with the UK government.

Others activists have called for an unofficial referendum to be held, similar to the disputed one in Catalonia in 2017.

Image copyright Getty Images Image caption A series of large pro-independence marches have been held across Scotland throughout the summer

Mr McEleny is expected to attempt to have a debate on Plan B added to the SNP conference agenda when the three-day event opens in Aberdeen on Sunday.

Speaking to BBC Scotland's The Nine ahead of the conference, Mr Neil added his voice to the calls for a Plan B to be adopted by the party.

The former health secretary said the SNP should seek a "written guarantee" from the UK prime minister that a referendum will be held if it wins the next Holyrood election.

If that guarantee is not given, Mr Neil said the party should effectively make the election the referendum. He added: "Assuming we win that election, then we would negotiate with the UK government an independence treaty".

He said there would then be a referendum on the treaty, regardless of whether or not the UK government gave permission.

'Our mandate is for independence'

Mr Neil added: "Scotland will not take no for an answer, so if they're not prepared to give us that democratic guarantee we can't just say that things will continue and we will go another another five years to try and get a referendum in 2026.

"If we get the mandate in 2021 then we are entitled either to have a referendum, if they are prepared to give us a Section 30, or if they refuse to recognise the democratic wishes of the Scottish people in those circumstances we are entitled to say we have the right to self determination.

"Therefore our mandate is for independence, not just for an independence referendum".

Ms Sturgeon, the Scottish first minister, has repeatedly said that a Section 30 order would need to be granted by the UK government to ensure the legality of any future referendum.

She told BBC Scotland earlier this week that the SNP would have to "demonstrate majority support for independence in a process that is legal and legitimate", and warned critics of her strategy that there was "no easy or shortcut route to independence".

She also pointed out that the SNP has previously won a majority of the Scottish seats in a general election on a minority of the votes - and argued that "nobody in Europe would listen to me in terms of the legitimacy of that" if she was to claim it was a mandate for independence.