Unionists must treat every election from now on as if Scottish independence is just around the corner, Scottish Liberal Democrat leader Willie Rennie has warned.

The SNP will keep calling referendums until they get the answer they want if Scotland continues to back nationalist manifestos, he told the party conference in Dunfermline.

And the UK Government would be duty-bound to deliver another referendum if Scotland expresses a clear preference for a nationalist party, he said.

The SNP has called for the right of the Scottish people to determine their own form of government to be enshrined in law in its submission to the Smith Commission on devolution.

But Scottish Secretary Alistair Carmichael, a fellow Lib Dem, said there are "some substantial disadvantages" in handing Holyrood the power to hold future referendums.

Westminster would have to consider the political context before it signed off on another "Edinburgh Agreement", he said.

The Lib Dem conference also heard from a nationalist Scottish Green representative who said substantial devolution would boost the case for another referendum, perhaps in 10 years, but a former Lib Dem MSP warned that too little devolution would also lead to calls for another referendum.

In his speech to conference, Mr Rennie said: "The growth in the nationalist movement must be a red warning that we cannot return to politics as usual. There must be no complacency.

"We must treat every election from now on as if independence could be round the corner.

"Voting for the SNP is no longer just a vote for an SNP government; it's a vote for independence. That's why they exist.

"They will keep on asking you the question until you give them the answer they want."

Later, Mr Rennie told the Press Association: "If you express a desire to have a referendum then there must be a mechanism for that to be delivered.

"There is a hazard now. The UK Government is not there to protect Scotland from another referendum.

"If people want another referendum to go independent then they should vote SNP and have it. If they don't want it, they shouldn't vote SNP."

Mr Carmichael urged new First Minister Nicola Sturgeon to stop "her manoeuvring for a second referendum that implies people were too stupid to get the answer right first time.

"This is a dangerous time for our country," he told the party conference.

"The long difficult years of austerity when people have seen their incomes squeezed as prices and other costs have gone up have produced fertile ground for parties offering easy answers.

"The forces of nationalism and populism have rarely been stronger - either the Scottish nationalism of the SNP or the English nationalism of Ukip.

"Telling people that all you need to do is draw a line on the map, pull up the draw bridge and all your problems will be solved - it is dangerous thinking and it is wrong.

Later, he told the Press Association: "On the question of (devolving power to hold) referendums, I could see some advantage but I could see some substantial disadvantages as well.

"It's difficult to imagine that wherever the power lies that you could ever have a referendum without Scotland's two governments agreeing to it."

When asked if Westminster should agree to it, he added: "You would have to wait and see what was in the manifesto and what the political context of the day was.

"But we had an Edinburgh Agreement for a referendum that would be fair, legal and decisive. We've had it, it's time to move on."

Lib Dem delegates later heard from former Scottish Green head of media James Mackenzie and former Lib Dem MSP Margaret Smith.

Mr Mackenzie said the Smith Commission is "the next step to independence".

"I certainly don't want the next 10 years of devolution, or however long it is until we get another referendum, to be another debate about which powers we need."

He added: "Scotland will be doing a lot more of its own self-governance, it will be building competence, demonstrating our ability to manage more powers responsibly and for me that feels like a basis for independence."

Ms Smith called on the Smith Commission to go beyond the "lowest common denominator".

"It's not going to be good enough to take small baby steps any more. This country wants settlement, stability, delivery on promises."

She added: "What if we fail? What if the next UK government fails to deliver?

"Then I believe we will be faced with a further referendum in the not-too-distant future, and the 45% will become the 55%."