DEPUTY First Minister John Swinney pledged to bring to an end the “moral obscenity of poverty” as he vowed to reintroduce the 50p income tax rate for the highest earners.

In a speech which repeatedly attacked the Westminster Government’s austerity cuts he told around 3,000 delegates at the party’s spring conference at Glasgow’s SECC that the SNP Government had put fighting inequality at the heart of its programme.

And with just over a month to go to the General Election on May 7, he said policies to create a fairer society should be extended to the tax system.

“The SNP Government is determined to deliver opportunities for every one of our people to make their way in the world,” he told the conference.

“And fairness extends to taxation. This afternoon our deputy leader Stewart Hosie will set out just some of the arguments we will make to deliver fairness at Westminster, some of the policies for which we will argue, including a return of the 50p rate of income tax for those earning over £150,000.”

According to party sources, the SNP manifesto committee would raise a further £675 million a year for the public purse across the UK.

It would also put the party in agreement with Labour which also wants to reintroduce the tax – and could be a key issue in any negotiations in the event of a hung parliament.

The 50p income tax rate was introduced towards the end of the last Labour government, but was abolished in April 2013by Tory Chancellor George Osborne, who cut the rate to 45p.

During his speech, which received a standing ovation, Swinney pledged the SNP in Holyrood would “fight tooth and nail’’ to protect vulnerable Scots from the “swingeing welfare cuts’’ imposed by Westminster.

He hit out at the UK Government’s austerity regime, arguing: “Lost growth and higher debt are just the financial costs of Westminster’s failure.

“The human cost has been higher still.Analysis by the Institute for Fiscal Studies found that the Coalition’s tax and benefit changes have hit the poorest households hardest.” “The disabled, the poor, the vulnerable have been targeted. That’s the reality of the Tory cuts.’’

Swinney also claimed that Labour and the Liberal Democrats were “up to their oxters in Tory cuts”.

He blasted the LibDems over their role in the Coalition, saying: “Danny Alexander and the Liberal Democrats have signed off on every pound cut, every budget slashed and every penny squeezed from the poor.’’

He added: “In 2010, Danny Alexander opposed a rise in VAT and opposed austerity. In Government he delivered both. No wonder the Liberals have no credibility the length and breadth of our country.”

Meanwhile, he said the UK Government had been cheered on by the Labour Party. “Labour and the Tories, joined at the hip – just like they were in the referendum – voting together for the Charter of Budget Responsibility,” he said.

“Ed Balls even said there was nothing in the Tories’ budget he would change.’’

“The Tories claim ‘we’re all in this together’. Well, the Liberals and the Labour Party certainly are.’’

The speech also sought to underline the SNP’s competence in running Scotland’s finances and its skill in managing large-scale infrastructure such as the new Forth road bridge.

“Since 2010-11, Scotland has suffered a cut of nearly 10 per cent in our budget – and closer to 25 per cent in the capital budget.

“That has been hard to manage. But we have maintained our public services, protected the NHS and, at the end of this financial year on Tuesday, I will balance our budget for the eighth consecutive year. That competence is one of the great strengths of your SNP Government.”