Scottish Conservative leader Ruth Davidson has accused the SNP of misleading the public over promises to not raise income tax during last year's Holyrood election.

Davidson made the charge to deputy first minister John Swinney, as he stood in for Nicola Sturgeon as she returns from a climate change conference in Germany, at the weekly session of First Minister's Questions.

The SNP pledged to freeze the basic rate of income tax, which most Scots pay, at the 2016 election.

Finance secretary Derek Mackay is widely expected to now raise income tax on some Scots in his forthcoming budget next month.

One change mooted in a Scottish Government policy paper on the subject would mean some of those who currently pay the basic 20% rate would pay more.

The Conservative leader reminded Swinney of his pledge not to "punish" low-paid workers before last year's vote.

She told MSPs: "The truth is the SNP wheeled out Mr Swinney, 'honest John', before the election to tell people that their taxes wouldn't go up and as soon as they got back in those promises turned to dust."

Swinney defended the possibility of an income tax rise in the forthcoming budget.

He said the devolved administration "is engaged in a substantive debate with members of the public about the real choices that are faced when you are in government, when you are trying to address the fact that public expenditure has been slashed by the United Kingdom government and that austerity continues to roll forward year by year".

The deputy first minister stressed the SNP would "act at all times to protect the interests of low-income individuals within our society".

He added later: "When the United Kingdom government slashed council tax benefit, this Scottish Government came to the rescue, this former finance secretary came to the rescue of low-income families within Scotland,.

"When the bedroom tax was applied by the Conservative government, this former finance secretary came to the rescue of low-income households in Scotland.

"So I am absolutely determined to make sure we stand shoulder-to-shoulder with low-income households in Scotland and take the right decisions to protect their incomes."