LABOUR will today unveil a hard-hitting poster claiming families will be £1100 worse off, on average, as a result of George Osborne's tax and welfare changes.

Labour and the Conservatives both sought to frame the election as a two horse race between their parties, after SNP leader Nicola Sturgeon shone in Thursday's seven-way televised debate.

On the stump in Glasgow, Jim Murphy, the Scottish Labour leader, said the TV debate had "made crystal clear the choice facing Scots at the general election" after viewers saw "seven passionate speakers but only two potential prime ministers".

Scottish Conservative leader Ruth Davidson sent the same message during a campaign visit to Musselburgh races.

"Our next Prime Minister will either be Ed Miliband or David Cameron," she said.

"That is the basic choice people face.

"And the fact is that when asked to choose between the two, most Scots prefer the Prime Minister."

Labour will train its fire on the Conservatives today when shadow chancellor Ed Balls uses a campaign visit to Yorkshire to highlight figures showing the impact of tax and benefit changes since 2010, including the rise in VAT, cuts to tax credits for working families and changes to the personal allowance which take effect next week.

Among a series of examples, the Institute for Fiscal Studies figures showed a two-earner couple with two children on average earnings will be £1700 worse off this financial year.

Mr Balls will say: "Labour's better plan will make fairer choices, put working people first and save our NHS."

Mr Murphy campaigned on Labour's pledge to ban zero hours contracts.

He joined a demonstration outside a Glasgow branch of sportswear store Sports Direct, a company that has been criticised for employing staff on zero hours contracts.

Describing the practice as a "scandal," he said: "David Cameron said never mind zero hours contracts.

"Well I do mind, Scotland minds and a Labour Government will ban exploitative zero hours contracts.

"Time is running out for bad bosses who rip off workers on zero hours contracts. Under a Labour Government working people will be guaranteed regular hours after 12 weeks of work."

He added: "Under the Tories working people in Scotland have been let down.

"In May Scotland is going to tell the Tories their time is up, but only a Labour Government is big enough and strong enough to kick them out.

"A vote for any party other than Labour simply gives David Cameron more time in Number 10."

He highlighted official figures showing 60,000 people in Scotland were employed on zero hours contracts, up 30 per cent of the previous year.

The Office for National Statistics figures showed Scotland saw the second biggest rise the number of zero hours workers in the UK after the West Midlands.

The STUC has warned the real total could be as high as 100,000.

Meanwhile Scottish Labour's deputy leader Kezia Dugdale stepped up the pressure on Nicola Sturgeon over the SNP's demand of full fiscal autonomy.

At First Minister's Questions on Thursday, the SNP leader refused to confirm her MPs would press for the policy given an opportunity to do so at Westminster.

The plan - which would make the Scottish Government entirely reliant on taxes raised in Scotland to meet its spending commitments - has been under fire since the Institute for Fiscal Studies think tank said it would blow a £7.6billion hole in the public finances if it were in place this year.

In a letter to Ms Sturgeon, Ms Dugdale wrote: "Given that full fiscal autonomy is the SNP's General Election demand, Scots deserve a straight answer to a very simple question.

"We have been very clear that the next Labour Government will introduce a Home Rule Bill within 100 days of taking office. Will the SNP seek to amend this Bill to include full fiscal autonomy?

"Your reluctance to champion a policy that is central to your General Election campaign will baffle many Scots.

"The only logical conclusion is that you know full fiscal autonomy within the UK would mean extra cuts to our NHS and schools worth £7.6 billion and cost 138,000 jobs in Scotland."

Ms Sturgeon said SNP MSPs would press for "maximum powers" for Scotland after the election when she was challenged at Holyrood.