The cabinet minister is today expected to accuse Nicola Sturgeon of treating the No vote a year ago as an “unfortunate but peripheral setback on the road to independence”.
However, Mr Mundell, the only Conservative MP in Scotland, will warn supporters of the Union that they have to continue “making the positive case for the United Kingdom”.
The Scottish Secretary claims that support for the Union is “broad and deep” in Scotland and that the Yes side’s defeat by a margin of 55 per cent to 45 per cent was a decisive result.
He says: “We’ve seen some big changes in Scotland as a consequence of the referendum.
“But my case today is that those changes are aftershocks of the referendum, and not – as some have argued – a symptom that independence is inevitable. Far from it. Independence is not inevitable.”
Mr Mundell will go on to claim that nothing decisive has happened to boost the case for independence in the last year.
He says: “Nothing that has happened since that decisive result makes independence inevitable.
“But for those us who support the United Kingdom, that has to mean making the positive case for the United Kingdom.”
The Scottish Secretary will also accuse the SNP leadership of attempting to “set aside” the result of the vote against independence and claim that the Union would need to be invented if it did not exist.
Mr Mundell will say: “The sovereign will of the Scottish people is set aside as though it counted for nothing and the First Minister openly acknowledges that she’ll try to hold a second referendum just as soon as she thinks she has a chance of winning it.”
An SNP spokesman, hitting back, said: “David Mundell’s claim that if the Union didn’t exist it would have to be invented is laughable – countless countries have become independent from Westminster rule in the last century, and not a single one has voted or chosen to return.
“The First Minister has repeatedly made clear that any decision on whether or not there is another referendum – and ultimately on whether or not Scotland ever becomes independent – will always be for the people of Scotland.”