FORMER prime minister Gordon Brown will make a rare high-profile appearance tomorrow when he helps launch Labour's campaign for Scotland to stay in the Union.

Brown, who led his party to defeat at the last General Election, will be the special guest at an event in Glasgow.

Although Labour has a dominant role in the cross-party Better Together campaign, senior party sources last year pushed for a separation to convey Labour's distinctive message.

Co-ordinated by the Scottish party's deputy leader, Anas Sarwar, the United with Labour campaign will stage its first event at the Emirates Arena tomorrow and is expected to contact more than half a million households over the next three months.

Sarwar said: "Our vision is for a fairer, better Scotland that stands strong within the UK, working in partnership with our neighbours.

"Constitutional politics brings together people who wouldn't normally be on the same side and we will continue to work with the Better Together campaign. But the Labour movement has a different view of Scotland's future from the Conservatives and Liberals.

"The referendum is the biggest decision the people of Scotland will face for 300 years and it is important that we have strong Labour voices speaking for the majority of Scots who believe we are better working together with our neighbours in the UK."

Sarwar and Scottish Labour leader Johann Lamont will make speeches at tomorrow's event, with Brown contributing.

The former prime minister has kept a low profile since he was voted out of office at the 2010 General Election, focusing on constituency and charitable work rather than making high-profile political interventions.

However, he is passionate about the Union and is expected to make appearances during the campaign.

Speaking last year, Brown accused the SNP of failing to answer key questions about independence: "I call it 'blank page nationalism', hiding the truth about the costs and risks of independence," he said. "A year-and-a-half into the debate the SNP started on independence, they are still refusing to answer the unanswered questions about what happens the day after the creation of a separate state."

Scottish Labour are also likely to have a plan in place for extra financial powers during the referendum. An interim report by its devolution commission made a case for devolving full control of income tax to Holyrood.

A senior source said the devolution plan is likely to form part of UK Labour's manifesto for the 2015 General Election, although the income-tax proposal is being resisted by some of the party's Scottish MPs

An SNP spokesperson said: "As long as the Tories are bankrolling the No campaign and leading it from Westminster, Labour will have an uphill struggle to convince their own supporters of their case, never mind the people of Scotland – and no amount of separate campaign launches will change that fact."

Deputy First Minister Nicola Sturgeon will tomorrow argue that there is a "natural majority" in Scotland for independence.

She will say: "I am convinced – from talking to people across the country – that there is a natural majority in Scotland for independence. What do I mean by that? I mean that people will vote Yes if we can persuade them that it opens the door to a wealthier and fairer country.