FIRST Minister's Questions descended into a shouting match after Kezia Dugdale, the Scottish Labour leader, accused the SNP of "standing shoulder to shoulder" with the Tories by refusing to raise taxes to protect public services.

Presiding Officer Tricia Marwick reprimanded MSPs for their "quite unacceptable" behaviour at the end of a fiery session dominated by Labour's plan to use Holyrood's existing tax powers to increase income tax by 1p across the basic, higher and additional rate, if it wins the election in May.

"Members should review the footage and consider whether they showed themselves and this parliament in the best light," the Presiding Officer said after exchanges were repeatedly drowned out by heckling.

In a rehearsal for the election campaign to come, Ms Dugdale said: "Nicola Sturgeon has built her career on telling us that more powers mean fewer cuts, yet she refuses to use the powers when it really matters.

"She has staked her reputation on improving education, yet she cuts school budgets rather than using the powers of the Scottish Parliament.

"Nicola Sturgeon has sold herself as the radical alternative to Tory austerity, but she has sold out the people who need her most."

Ms Sturgeon claimed Labour's plan was unfair and would increase taxes for everyone earning over £11,000 per year.

"Tax rises on the lowest-paid in our society is not standing up to Tory austerity.

"It is transferring the burden of Tory austerity on the shoulders of those who can least afford it," she said.

The clashes came as Alex Bell, a former senior policy adviser to the SNP, questioned its decision to retain UK tax rates.

He wrote in a newspaper column: "They (the SNP) have built popularity on the idea that flaming cuts are licking across the border and only they can fight the inferno – but they refuse to hit the sprinklers, in the form of a tax rise.

"If you spend your life shouting “fire, fire”, at some point you have to use the extinguisher. If not, then you just look like an arsonist."

Later, questioned by ScotsTory leader Ruth Davidson, Ms Sturgeon refused to rule out future increases when - or if - Holyrood gains full control over in income tax rates under the Scotland Bill.