Mundell claims Scotland population could grow following further devolution amid criticism from opposition

The population of Scotland could increase as a result of its new powers over welfare and tax according to the Scottish Secretary David Mundell.

Mr Mundell argued this could be a consequence of economic growth brought about by greater devolution.

However, the SNP said he was avoiding his duties in respect of the new powers. He told SNP MSP Ronnie Cowan that the powers in the Scotland Bill “create the opportunity for Scotland’s economic growth to increase and for Scotland’s population to increase”.

Eilidh Whiteford, another SNP MP, described the fact Mr Mundell was not present at negotiations on the amount of money to be transferred from London to Edinburgh as “bizarre and frankly quite unacceptable”.

The two governments will hold talks tomorrow on the fiscal framework which will underpin the powers.

Already, there have been five meetings between Deputy First Minister John Swinney and Conservative Treasury Minister Greg Hands.

But Ms Whiteford questioned Mr Mundell on why he has been considered “irrelevant” to the discussions.

He rejoined: “I know it may impinge on the self-importance that some SNP MPs attribute to themselves but it is the Deputy First Minister of Scotland, John Swinney, who is negotiating the agreement not SNP MPs.”

Ian Murray, Shadow Scottish Secretary, accused Mr Mundell of keeping the talks secret and warned Scotland is being “kept in the dark” on the future powers.