The Scottish Secretary has demanded clarity on the SNP's position on a second referendum as the party's chairman confirmed that independence will be on the agenda at its forthcoming conference.

David Mundell, Scotland's only Conservative MP, who was appointed to lead the Scotland Office in May, has urged SNP leader Nicola Sturgeon to make absolutely clear what her party's plans are amid several indications by nationalist MPs that there will be another referendum.

Former SNP leader Alex Salmond said yesterday that a second referendum is "inevitable", a view echoed this morning by party chairman Derek Mackay.

Mr Mackay, business convener for the SNP conference in Aberdeen, said the party's manifesto has not been written but confirmed independence would be talked about at the conference.

He reiterated Ms Sturgeon's statement that a second referendum will take place if there is a material change in the political circumstances and Scotland votes for a party promising another referendum in its manifesto.

But Mr Mundell told BBC Radio Scotland's Good Morning Scotland programme that it is not for the SNP to decide when Scotland wants another referendum.

He said: "I don't think that it's for the SNP to determine whether the people of Scotland want another referendum.

"Ultimately it will be for the people of Scotland to determine whether there is another referendum but it won't be for the SNP to tell the people of Scotland what they think on that issue."

He added: "What I want to see is the clarity of the SNP position. At the moment we've got Alex Salmond pushing for a second referendum, we've got Nicola Sturgeon not being very clear at all what her position is.

"I want them to be absolutely clear with us what their position is on having a second referendum. They've said repeatedly that there isn't going to be a second referendum at official level; now we see all these MPs, Alex Salmond himself pushing for a second referendum. Nicola Sturgeon needs to be absolutely clear.

"I don't think that it is for the SNP themselves to determine whether the people of Scotland are in favour of having another referendum."

The Scottish Secretary has said there are no contingency plans for the possibility of a further referendum on independence after next year's Holyrood elections.

With opinion polls pointing to the possibility of a SNP landslide in the Scottish Parliament elections, the move sparked speculation a second vote could be on the cards, despite Scots rejecting independence by a majority of 55% to 45% in last September's referendum.

Mr Mackay told BBC Radio Scotland: "We will have a party conference and we will have a Scottish parliamentary election, and in that election we will have a manifesto that we believe will represent the people of Scotland, and that manifesto will then be presented to the people and they can choose.

"I can't tell you what's in the manifesto because it clearly hasn't been written yet."

In response to Mr Mundell's call for clarity, he said: "I can give you that clarity - we are not planning for or preparing for a second referendum but we still believe in independence for Scotland."

He added: "At this point in time I don't think the circumstances are presentable for another referendum right now.

"I'm not going to speculate about what is going to be in the manifesto.

"We will certainly talk about independence because we still believe in it and of course we think that is the right way to go and that is the direction of travel, more powers and ultimately independence for Scotland."

Shadow Scottish secretary Ian Murray said: "Everyone agreed back in September when the referendum happened that this would be a once-in-a-generation opportunity, even a once-in-a-lifetime opportunity.

"So to suggest that this may be in the SNP manifesto in just a few months' time I think would be wrong."

He added: "What Derek Mackay didn't commit to was that it wouldn't be in the 2016 Scottish parliamentary election manifesto for the SNP."