NICOLA Sturgeon has insisted Scotland’s lowest earners must be protected from any changes to income tax, hinting at hikes for the better off.

The First Minister outlined four “tests” that should be met before tax rates are altered – including ensuring any adjustments “make the tax system more proportionate and progressive”.

She will today detail potential approaches the Government could take in the future, calling on other parties to “put aside party interest for the national interest”.

But the Scottish Conservatives argued any hike would harm the economy, resulting in lower tax revenues to help pay for schools and hospitals.

Shadow finance secretary Murdo Fraser said: “Our position simply is that Scotland should not have higher taxes than the rest of the United Kingdom.”

The Scottish Government set out plans to examine the role of income tax in the budget earlier this year.

Ms Sturgeon said any changes “must not cause harm to our economy”, while public services should be maintained and promoted.

But she said: “Against the backdrop of continued UK austerity which will see Scotland lose £2.9bn from our budget over a 10 year period, rising costs as a result of inflation, an ageing population and with the prospect of a deep and damaging Brexit on the horizon, it is important that as a parliament and as a country we begin a debate about how we support our economy and fund public services for the future.”

A paper published today will set out four alternative suggestions for the future of income tax.

Ms Sturgeon said: “Income tax is one of the few tools the Scottish Parliament can use to change the size of the Scottish budget, but it is limited in its scope.

“More than 60% of our spending power is determined by decisions taken at Westminster.

“So the debate needs to be about more than filling the gaps created by Westminster austerity or parties trying to outbid each other.”

She insisted the alternative approaches “are not fixed positions or government proposals, but starting points for a discussion”.

Scottish Labour business manager James Kelly called for tax powers to be used “to end the cuts to local government, which have totalled £1.5 billion since 2011”.