THE umbrella pro-Union campaign will launch before the summer and hopes to match the £2 million war chest the SNP has already accumulated, The Herald can reveal.

While each of the three pro-Union parties will launch their own discrete campaigns, they will come together to form what one senior figure described as a "wide-ranging political and civic, cross-party, cross-Scotland campaign" to fight for the nation to remain part of the UK.

With First Minister Alex Salmond having already announced the pro-independence campaign will launch shortly after the May local elections, pressure has been mounting for the pro-Union forces to announce their own intentions.

At present, there is no official name to the umbrella pro-Union campaign and, unlike the pro-independence one, it will not have a single figurehead. Instead, a number of politicians, including Labour's Alistair Darling and Johann Lamont and the Liberal Democrats' Charles Kennedy and Willie Rennie, will front it.

A Scottish Labour source made clear his party will be the main player in the umbrella campaign with the Tories playing something of a secondary role. He said: "We expect to play a prominent role and are very much driving this. This will be a very broad campaign and not just involve politicians. What will surprise people is the depth and diversity of support, which will contrast with the narrowness of the support in favour of separation.

"The Nationalists have been unable to break from their core support while we are very keen to break out from the political elite and engage the people of Scotland."

Asked if the umbrella pro-Union campaign would hope to match the £2m the Nationalists have so far received to promote independence, the source added: "Yes, we're hopeful of doing that. The SNP outspent us in 2011 but we outspent them in 2010."

At Scottish Labour's recent conference, Ms Lamont pointed out: "The skills of the Labour campaign will be leant to an all-party campaign when they are needed."

Last month during a visit to Scotland, David Cameron admitted the pro-Union forces were playing catch up and had to do more to galvanise support.

One senior Conservative made clear the umbrella pro-Union campaign would be launched "before the summer", ie between mid-May and mid-June, and the aim of each of the three pro-Union parties would be to maxi-mise the vote from each of their respective support bases.

Later this month, the Scottish Conservatives will launch their own Friends of the Union campaign at their party conference in Troon with the Prime Minister and Scottish Tory leader Ruth Davidson being at its forefront.

Last night, David Mundell, the Scotland Office Minister, told The Herald: "The cross-party campaign will make the positive case for Scotland staying in Britain. It will be entirely positive, focusing on the benefits Scotland gets in staying in the UK. It will be bringing people from all parties and none to make that case."

Asked if the pro-Union campaign will have sufficient funds and if Lord Ashcroft, the Tory benefactor, might be among the contributors, he replied: "There are a lot of people who want to keep Scotland in Britain and will donate to the campaign."