Gloves come off in battle to win over 200,000 Scots who could decide general election

In his first major speech of the campaign, Jim Murphy, the Scottish Labour leader, will reach out to voters who turned their back on his party in 2010 and voted Yes in September's independence referendum.

Meanwhile SNP leader and First Minister Nicola Sturgeon will appeal to No voters who want more powers for Holyrood.

In an open letter released today, she says only a strong block of Nationalist MPs would guarantee further devolution, a cause, she says that could unite Scotland.

As MSPs prepare to return to Holyrood after their festive break the main parties are all stepping up their election efforts four months out from the May 7 poll.

The Conservatives and Labour enter the race neck and neck in the polls, raising the prospect of a hung parliament.

The SNP are on course to make huge gains if they can maintain a 20 point lead over Labour in Scotland.

Ms Sturgeon believes they could deny Labour an overall majority and emerge from the election holding the balance of power.

In his speech today, Mr Murphy will reach out to 190,000 Scots he describes as "the most important voters in the UK".

The group voted Labour in the 2010 Westminster election but failed to turn out for the following year's Holyrood poll which the SNP won by a landslide.

They voted Yes in the referendum and most, according to Labour's research are older men living within 25 miles of Glasgow.

Addressing supporters at Edinburgh's Our Dynamic Earth museum, Mr Murphy will say: "They voted yes largely because they wanted rid of the Tories and wanted change.

"Now they can decide whether to vote Labour to get rid of the Tories or to vote SNP and keep the status quo.

"At the General Election these will be the most important voters in the UK.

"They will decide whether to hand David Cameron his P45."

The new Scottish Labour leader will devote a large section of his speech to discussing global insecurity and economic uncertainty, in a coded message that independence would not cure Scotland's ills.

The 190,000 target voters will each be sent personal letters during a "January offensive" to win them over.

Presenting her key election message today, Ms Sturgeon says: "If you voted No but support a home rule Scottish Parliament - a vote for the SNP is the only way to deliver it.

"Even if you don't normally vote SNP at Westminster, lend us your vote this time so that we can hold Westminster to account and make Scotland's voice heard."

She says the issue "provides an opportunity for us to unite as a country" and dismisses Mr Murphy's claims than an SNP vote could usher in a Tory government as "an insult to the intelligence of the Scottish people" after Labour won the 2010 poll in Scotland by a wide margin but slumped to defeat across the UK as a whole.

The SNP step up their campaign today with a series of newspaper ads depicting a a long rank of tartan benches in the House of Commons.

The adverts says: "The more seats we have here, the more powers we'll have in Scotland."

Meanwhile the Scots Tories have claimed Nicola Sturgeon and Labour leader Ed Miliband are already "half way down the aisle" towards a political marriage.

In a letter going out to supporters today (Mon), Scots Tory leader Ruth Davidson accuses the SNP of using the general election to force a re-run of last year's independence referendum.

She writes: "Nicola Sturgeon may have spent the referendum campaign saying she didn't believe in Westminster and no longer wanted Scotland to send any MP's to the House of Commons, but suddenly she's changed her tune.

"She's talking up an electoral pact between Labour and the SNP, with Alex Salmond heading back to London to seal the deal.

"The election is another four months off, and yet Nicola Sturgeon and Ed Miliband are already half way down the aisle.

"Think what it would mean - a weak Ed Miliband as Prime Minister with the SNP pulling the strings."

Setting out her core election message, she says the Conservatives are "the only party which can keep us on track" to rebuild the economy and thwart SNP efforts to stage a second independence vote.

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