The SNP has accused Labour of presiding over years of council-tax hikes and planning further tax rises for the low-paid as the nationalists were urged to support a tax on very high earners.

Labour has dismissed Nicola Sturgeon's concerns that a 50p tax rate could cost Scotland £30 million through tax avoidance as "smoke and mirrors", insisting HMRC has the power to make sure Scots pay their taxes.

Ms Sturgeon claimed Labour were planning "tax hikes on the low-paid" and accused them of presiding over "exorbitant" council-tax rises while in government.

Meanwhile, Willie Rennie has given a "guarantee" education funding will rise under a Liberal Democrat Scottish government - but ruled out ring-fencing, which means he cannot ensure councils will spend the uplift on education.

The Scottish Greens have pledged to support the food and farming sector, and also tackle poor nutrition and food poverty, with a Food, Farming and Health Act.

Labour's shadow Scottish Secretary Ian Murray said: "Nicola Sturgeon is using smoke and mirrors to justify not backing a 50p top rate of tax.

"When schools and local services across Scotland are facing hundreds of millions of pounds of cuts, the SNP will not ask some earning over £150,000 a year to pay a penny more in tax. That's not the mark of an anti-austerity party."

Ms Sturgeon reaffirmed the SNP's commitment to free prescriptions on the day such charges increase to £8.40 in England.

The SNP said its policies stand in contrast to "Tory plans for hidden taxes on health and education, Labour plans for tax hikes on the low-paid and further cuts from a UK Tory government".

Ms Sturgeon said: "While Labour plan to hit one million low earners with tax hikes and the Tories want to tax essential services like healthcare and education with tuition fees and prescription charges, the SNP is providing the protection family incomes need during tough financial times.

"We've abolished prescription charges - and will resist any attempt from the Tories or any other party to re-introduce them."

The Lib Dems want to put 1p on income tax to fund a "pupil premium" worth £1,400 for primary pupils who require extra support and £900 for secondary pupils from disadvantaged backgrounds.

Asked if the Lib Dems would guarantee a real-terms increase in education funding on BBC Radio Scotland's Good Morning Scotland programme, party leader Mr Rennie said: "Yes, we would."

He would not guarantee that local authorities would ring-fence the cash but insisted they "would see the sense" of using the money to invest in education.

Mark Ruskell, food and environment spokesman for the Scottish Greens and MSP candidate for Mid Scotland and Fife, outlined plans for the party's Food, Farming and Health Act.

He said: "Scottish Greens see the connection between a healthy, well-nourished population and a thriving, resilient economy.

"While others are happy to let market forces steer our country's food policy, Greens believe it's time for a bolder Holyrood that properly addresses the scandal of food poverty in food-rich Scotland."

The deadline to stand as a candidate in the Scottish Parliament election will close on Friday afternoon.

A final list of those seeking election on May 5 will be determined after the official Holyrood nomination period ends at 4pm.