The Scottish Government cannot credibly tackle inequality while proposing only tax cuts, MSPs have been told.

Ministers cannot continue to highlight the impact of spending cuts without also considering an increase in taxes, according to the Scottish Trades Union Congress (STUC).

The Scottish Parliament will have responsibility for a Scottish rate of income tax (SRIT) from April next year and MSPs are examining whether to keep the rate the same as the rest of the UK, raise it or lower it.

In a submission to Holyrood's Finance Committee, the STUC said: "In the longer-term, raising total tax revenues as a percentage of GDP is necessary to support the more equal, fair and democratic society desired by both the Scottish Government and the STUC."

Assistant Secretary Stephen Boyd told the committee the STUC wanted the rate to remain at 10p in 2016-17 because of the prevailing economic circumstances but would "feasibly" back an increase in the future.

He attacked the argument that policies such as the small business bonus scheme and proposed cuts to air passenger duty (APD) would boost the economy and job creation, and therefore increase tax revenue.

Mr Boyd said: "I don't accept that all. I would argue very strongly the evidence from all countries is that when you cut taxes, detriment in revenues is immediate and real, economic outcomes are highly uncertain and if they transpire at all then they are long-term.

"We have been calling for evidence to be produced that describes to us in detail the benefits that the small business bonus has brought to the economy. It has never been forthcoming.

"In terms of air passenger duty ... I would be surprised if there's a significant employment dividend."

He added: "That constant refrain about we could achieve tackling levels of inequality on the basis of total tax revenue in Scotland not increasing, I think, is unhelpful to the kind of debate we would want to see."

The committee also heard from Dr Gerry McCartney, head of public health observatory at NHS Health Scotland, which has argued for income tax to be increased in Scotland to help tackle health inequalities.

He told MSPs he recognised the powers coming to Holyrood next year are "blunt", with greater controls over income tax still to be devolved as a result of the Smith Commission.

Dr McCartney added: "The Scottish Government since 2007 and previous administrations have committed to reducing health inequalities and yet health inequalities in Scotland are stubbornly high.

"I think there is a strong case to do something soon, something urgent, something now to increase the SRIT, but use that revenue to ensure that people on lower incomes are not penalised.

"If we continue to wait and not use those powers that are available to us, we do run the risk that things will be an awful lot worse by the time we get round to discussing what we are going to do with more powers."