Scotland's population could get a boost from sweeping new powers over tax and welfare, Scottish Secretary David Mundell has claimed.

Scotland’s only Tory MP predicted the outcome could result from economic growth triggered by greater devolution.

But he faced accusations from the SNP that he was neglecting his duties over the powers.

Under questioning Mr Mundell told SNP MP Ronnie Cowan that the new powers included in the Scotland Bill going through parliament "create the opportunity for Scotland’s economic growth to increase and for Scotland’s population to increase”.

But the SNP's Eilidh Whiteford said that Mr Mundell's absence from negotiations on how much money will be transferred between London and Edinburgh in the future was "bizarre and frankly quite unacceptable".

The UK and Scottish Government are next due to holds talks on the controversial ‘fiscal framework’ which will underpin the new powers in Edinburgh on Friday.

Experts have warned that the wrong deal could cost Scotland billions over the next decade.

There have already been five meetings between the Conservative Treasury Minister Greg Hands and Scotland's Deputy First Minister John Swinney.

But Ms Whiteford asked Mr Mundell why he has been deemed "irrelevant" to the negotiations.

Mr Mundell replied: “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."

Shadow Scottish secretary Ian Murray also accused Mr Mundell a sham by keeping the negotiations secret and warned that Scots were being "kept in the dark".

Meanwhile, the chair of the UK Government's public finance watchdog warned that Scottish ministers stamp duty forecasts are based on an "optimistic" view of property prices.

Robert Chote, from the Office for Budget Responsibility (OBR), was giving evidence to MSPs on the differences between his organisation's predictions for the new Land and Buildings Transaction Tax (LBTT) and the Sottish Government's.