HOLYROOD could gain a "minimum set" of new powers soon after the 2015 General Election if Scots reject independence in the forthcoming referendum, Gordon Brown has said.

The former Labour prime minister said there was "scope for agreement" between the three main pro-UK parties on further devolution, despite wide differences on handing ­Holyrood control over income tax.

Mr Brown raised the prospect of legislation early in the life of the next UK parliament as he launched a new phase in Labour's referendum campaign.

In a significant shift, senior Labour figures will urge Scots to be proud to vote No - a negative word that the campaign has tried to avoid up in its slogans until now.

Mr Brown was responding to Conservative plans to make Holyrood responsible for raising income tax north of the Border, with powers to set the rates and bands.

A similar proposal has been put forward by the Lib Dems but both parties have gone further than Labour, who plan to give MSPs powers to increase, but not cut, the higher rates of income tax relative to the base rate.

The policy was designed to prevent the country from becoming a "tax haven" for high earners from the rest of the UK, Scots Labour leader Johann Lamont has said.

The three parties have also made contrasting pledges on other powers to be devolved to Holyrood in areas which include welfare and economic development.

Prime Minister David Cameron and Mr Brown have spoken of wanting to build cross-party consensus before legislating.

Mr Brown said: "There is ­agreement on more ­accountability for the parliament and that is at the heart of all three reports.

"I think there is scope for agreement about the kind of powers that could be devolved both for policy and for accountability and for taxation." He added: "There is an agenda for change that can be supported at least in part by the other parties

"The issue that is interesting is that the Conservatives and the Liberals are now supporting a more extensive devolution agenda that is also similar to the one that is being promoted by Labour.

"That answers the charge that there will be no action after September.

"We know now there is an agreement at least on a minimum set of changes that would happen after September and that could mean the early delivery of further devolution."

Mr Brown was speaking at the launch of a new phase in his party's United with Labour referendum campaign.

The drive will attempt to rally traditional Labour supporters behind a vision of a fairer Scotland as part of the UK.

Mr Brown is to undertake a series of town hall meetings across the country, addressing 5000 people over the next fortnight.

Labour also broke new ground by unveiling badges with the slogan "No thanks" and a pledge card, giving five reasons to stay in the UK, bearing the message: "I'm voting No."

A spokesman for First Minister Alex Salmond said: "It is clearer than ever that only a Yes vote in September can deliver the powers Scotland so badly needs.

"Labour have been outbid by the Tories on their more powers offer - and whatever Gordon Brown claims, there is next to no prospect of a meaningful cross-party agreement between the Westminster parties before the referendum.

"A Yes vote is the only way to guarantee we deliver the powers all the Unionist parties now say are needed."

l Gordon Brown joked he was enjoying the referendum campaign more than his time as prime minister.

Asked during a press ­conference yesterday how the different challenges compared he replied: "I'm enjoying this campaign."

Laughing, he added: "The Press is so much kinder to me."