SNP leader John Swinney is offering Scots a “cast iron guarantee” his party’s MPs will “fight to protect Scotland’s values” at Westminster.

He is making the commitment in the wake of warnings that spending cuts are coming, regardless of whether Labour or the Tories win next month’s General Election.

The Institute for Fiscal Studies think tank has warned both main Westminster parties are “avoiding the reality” that their plans lock them into “sharp” spending cuts.

Mr Swinney, meanwhile, has already argued public spending is the defining issue of the election campaign.

John Swinney has repeatedly warned that spending cuts are looming, whoever wins the General Election (Jane Barlow/PA)

The Scottish First Minister will raise the issue again as he campaigns on Wednesday, telling voters: “At this election only a vote for the SNP is a vote to protect Scotland’s values.”

He declared: “While Labour and the Tories take their orders from bosses in London, the SNP will always lead for Scotland, not be led by Westminster.

“Today, I am reiterating that commitment to the people of Scotland – our cast iron guarantee that SNP MPs will always fight to protect Scotland’s values in the face of further cuts at Westminster.”

Mr Swinney will highlight how the SNP has “used its limited powers at Holyrood to build a better nation”,  pointing out Scots benefit from policies such as free tuition fees, free prescriptions and the Scottish Child Payment benefit, none of which are available south of the border.

He added that those measures had been introduced despite Westminster having “inflicted over 14 years of cuts to public services, a Brexit that Scotland overwhelmingly didn’t vote for, and a cost-of-living crisis of the Tory party’s own making”.

Mr Swinney claimed: “There isn’t a household in Scotland that hasn’t felt the sharp end of these decisions.

“But, while Westminster chaos has caused misery for Scots, the SNP has used its limited powers at Holyrood to build a better nation.

“We’ve scrapped tuition fees and prescription charges, supported people in the face of rising bills and household costs, and introduced the Scottish Child Payment designed to support low income families – one of several policies expected to keep 100,000 children in Scotland out of poverty this year.”

The First Minister continued: “These game-changing policies show that decisions designed to benefit the people of Scotland, are best made in Scotland.”