Tory leader Ruth Davidson has been accused of planning "hidden taxes" for Scots after she said students could have to pay about £6,000 after completing a four year degree.

Ms Davidson also said her party wanted to phase prescription charges - which were scrapped by the SNP administration - back in north of the border, saying these could rise to "about £8".

The Conservatives are the only party fighting the Holyrood election with a commitment not to raise income tax once MSPs get the power to do this in April 17.

But after she told the STV Scotland Debates programme about the Tory proposals on prescription fees and charging graduates, SNP leader Nicola Sturgeon said: "You're not the party of low taxes, you're the party of hidden taxes."

While Ms Davidson came under fire for this, the SNP leader was attacked after she hinted Scotland could have a second independence referendum after May's Holyrood elections.

Ms Sturgeon has been repeatedly pressed on whether her manifesto for the election will include a commitment to another vote on the country's place in the UK.

She told the audience in Edinburgh: "My manifesto, in essence, will put this decision in the hands of the people where it should be.''

Scottish Labour leader Kezia Dugdale pledged her party's manifesto would "rule out another referendum for the lifetime of the next parliament".

She insisted: "I will represent the vast majority of people in this country who voted no in the belief that it was a once-in-a-generation opportunity.

"With Labour there will not be support for a second referendum on independence, that's a guarantee."

Meanwhile Ms Davidson said the First Minister was keeping the country "on a knife edge" over a future referendum, arguing: "What people in Scotland want is a period of stability and calm like they were promised."

In the section of the debate where Ms Davidson was cross-examined by her rivals on Tory policies, she said her party would charge students "just over £1,500 a year" for university education, which would be paid after they had graduated and started earning.

Asked about charges for university students, Ms Davidson said: "It's not a graduate tax, it's a contribution after you have graduated and once you are earning money. We expect it to be within the region of just over £1,500 a year that you are at university, so that's a lot less than England."

She hit back at Ms Sturgeon, saying: "You keep talking about the cost of university education being free. Do you know what is the cost of university education, the cost is 152,000 college places, the cost is the fact that poor people in Scotland are half as likely to be able to get into university as south of the border."

The Tory also defended plans to end free prescriptions in Scotland, saying: "The difference between you and me Nicola is I'm happy to pay for paracetamol in order that someone on a cancer ward can get a cancer drug they can get down south that they can't here."

A Scottish Conservative spokesman said afterwards: "As we've made clear throughout the last few years, we support a moderate graduate contribution after students leave university and are earning a good wage."

"As Ruth says, we believe a figure of £1500 a year is a fair sum - with the money being invested back into our education system and bursaries for the poorest students."

Ms Dugdale later stopped short of saying if her party would campaign alongside the Conservatives again if there is a second referendum.

UK leader Jeremy Corbyn has blamed the party's role in the cross party Better Together campaign for Labour's fall in support north of the border, which saw it lose all but one of its MPs in last year's Westminster election.

Ms Sturgeon asked her rival if she regretted campaigning with the Conservatives, as she called on her to "take the opportunity to apologise" for this.

Ms Davidson also joined in the questioning, saying: "If there was ever another referendum I would stand shoulder to shoulder with you again. Would you do so with me?''

But Ms Dugdale told the Tory: "The country's future I think lies beyond constitutional politics. I think regardless of whether you voted Yes or No you should vote Labour because we believe in using the powers of the parliament to end your government's austerity.''

With Holyrood getting new powers to set income tax rates and bands from April 2017, the leaders of all five of Scotland's largest parties were involved in heated exchanges over what has become a central issue in the election campaign

Ms Sturgeon insisted the point of income tax is to raise revenue for services, and said: ''My tax proposals will do that.''

But the SNP has rejected increasing the top rate of income tax to 50p in 2017-18, arguing such a move could cost £30 million.

Ms Dugdale challenged her on this: ''You won't ask rich people to pay a penny more.''

She hit out at the First Minister, saying: ''Nicola says her plans raise £2 billion - actually you need to raise double that to stop the cuts.

''If she is not prepared to raise that amount of money she cannot feasibly say she is against austerity.''

Labour backs a 1p rise in the basic rate of income tax in Scotland, and also wants to restore the top rate of tax - paid by 17,000 people in Scotland earning £150,000 a year or more - to 50p.

Ms Davidson said all four other leaders ''want to raise taxes on the hard working people of Scotland'' promising the Tories would ''fight to keep more money in the pockets of the workers of Scotland''.

She insisted taxes should be about raising cash for public services ''not punishing people that earn money''.

But Liberal Democrat leader Willie Rennie said: ''Ruth has just talked about cutting taxes, she only really wants to cut taxes for the rich, she doesn't want to improve services for anybody else.

''I want to make a transformational investment in education so it is the best in the world again.''

The Lib Dems plan a 1p rise in the basic rate of income tax, which they say would raise almost £500 million for education, with the money to go to schools, nurseries and colleges

Mr Rennie added: ''Nicola Sturgeon has bellyached about austerity and when she finally gets the chance to do something about it she is frozen to the spot, she's not seizing the opportunity to do something radical, transformational.''

Meanwhile Scottish Green co-convener Patrick Harvie said: ''Taxation isn't just an accounting mechanism to ensure we fund public services, it should also be about income and wealth inequality in our society because our economy belongs to all of us.''

The Greens want to raise the top rate of income tax to 60p for the very highest earners, but say most taxpayers would be better off under the party's plans.