THE SNP has launched a furious attack on Scottish Labour over the party's promised tax hikes.

John Swinney, the SNP's Deputy First Minister, said Labour's plans were

"unfair, unworkable and simply indefensible," as the parties' row over tax continued to dominate the election campaign.

Kezia Dugdale, the Scottish Labour leader, will hit back today when she claims tax rises are essential to protect Scotland from cuts to education spending.

Labour plans to increase the basic and higher rates of income tax by 1p, and the additional rate, paid by those earning over £150,000, by 5p.

Mr Swinney said Labour were "determined to hit the poorest in our society with the cost of Tory austerity" and accused his opponents of failing to explain a proposed rebate scheme designed to protect the poorest for increases in the basic rate.

The SNP has faced days of criticism from both left and right over its own plans for modest tax cuts in 2017/18, when Holyrood assumes almost full control over income tax.

In a robust defence of the plans yesterday, Mr Swinney said: "The SNP will protect low earners from paying the price of Tory austerity.

"An SNP Government will not increase tax on the 2.2 million basic rate taxpayers or on the half a million pensioners in Scotland on low incomes."

But Ms Dugdale will today highlight a sharp fall in the number of trainee teachers since 2007 as she presses the case for greater investment in schools.

During a visit to a nursery in East Lothian, she will say: "Nicola Sturgeon used to agree that the richest should pay their fair share, but now she thinks it would be reckless and refuses to use Holyrood's new powers to make it happen.

"We need to cut the gap between the richest and the rest in our classrooms but that won’t happen with the SNP cutting the budget for schools."

Tax has dominated the opening days of the election campaign and is expected to spark fresh clashes tonight when STV broadcasts the second leaders' debate from Edinburgh.

The Scottish Greens will unveil their tax plans, including new income tax rates and bands and a replacement for council tax, this morning.

Labour also came under fire from the Scots Tories, who described Ms Dugdale's pledge to guarantee an appointment at a GP surgery as "a shambles" because patients would not automatically see a doctor.

Labour dismissed the claim, insisting it had always been clear patients would see the most appropriate person at the surgery, who might be a doctor or specialist nurse.

On the campaign trail yesterday, the SNP and Scottish Liberal Democrats both focused on their promises for school leavers.

Visiting communities near the Dalzell Steelwork in Motherwell, North Lanarkshire, Nicola Sturgeon highlighted her party's pledge to increase the number of apprenticeship training places from 25,000 a year to 30,000 a year by 2020 if re-elected on May 5.

She said the 5000 extra places would be in high level science, technology and engineering.

The Liberal Democrat leader, campaigning in Aberdeenshire East highlighted plans to invest extra cash in colleges.

The LibDems, who also plan to increase the basic and higher rates of income tax, have pledged to spend the £475million per year raised on education.