Gordon Brown has insisted it is inevitable that the Scottish parliament will quickly gain significant new tax and legal powers after a clear consensus emerged between the main UK parties.
The former prime minister said David Cameron's support on Monday for proposals to give Holyrood power over income tax rates had created political momentum for far more devolution, if Scotland's voters rejected independence in September's referendum.
"There's now all-party support, including the Conservatives and Liberals, making it possible for the early delivery now of big changes in the constitution by agreement between the different parties," Brown said at the launch of Scottish Labour's referendum campaign.
"We should devolve powers that we've not so far devolved."
Four years after his defeat following Labour's disastrous general election campaign in 2010, Brown has become a dominant figure in the party's official pro-UK campaign, United with Labour. Despite his troubled UK premiership, Brown remains popular in Scotland.
As the main referendum campaign gathers pace. Brown has toured Scottish towns and cities this week, speaking in Glasgow, Dundee, twice in Fife, Edinburgh and Aberdeen, as well as publishing a book on Scotland's place in the UK.
The party is also planning a series of "town hall meetings" involving senior UK shadow cabinet ministers including the shadow Scotland secretary, Margaret Curran, the shadow foreign secretary, Douglas Alexander, and former Cabinet members including former defence and home secretary John Reid.
Brown said the current consensus was in contrast to the collapse of Labour's Scottish home rule proposals in 1979 and the unfulfilled promises from Margaret Thatcher about further prospects of devolution. It took until 1999 for a Scottish parliament to be established.
Nicola Sturgeon, the deputy first minister of Scotland, and the Scottish National party repeatedly cite that period as proof that Westminster cannot be trusted in a bid to undermine the UK's parties alliance against them.
Brown said the recent cross-party consensus on greater powers – above and beyond new powers to control income tax up to 10p in the pound already coming into force in 2016, meant that a substantive deal could be reached. Some agreement on a faster timetable could be reached in the next few months, he suggested – a proposal that has already been rejected by Ruth Davidson, the Scottish Tory leader.
"These measures I believe could be agreed between the parties to be put in legislation as soon as is practicable," he said, attempting to play down suggestions that the process for agreeing and implementing extra powers could take the rest of the decade.
"And therefore, it can never be said in future that as after 1979, there was no change for many years. It is inevitable with the agreement between the parties that we can get the early delivery of the proposals."
Brown rejected the suggestion there was a large gulf between Labour and the Tories on how much control Holyrood would get over income tax. Labour proposes giving Holyrood power over 15p in the pound, and be barred from cutting rates below the UK's.
The Tories want Holyrood to have full control, including the freedom to cut taxes and the right to have new, variable rates. The most important issue was that the parties agreed on the principle of income tax devolution and agreed that income tax reliefs remained at UK level, he said.
The Tories have also said savings, share dividends and pensions should be excluded, and have offered conditional support to Labour's proposals to devolve housing benefits to Holyrood – worth some £1.7bn a year.
He said it was "ridiculous" to suggest that Labour had been outbid by the Tories on income tax, insisting that Labour also wanted to hand over powers to implement higher taxes on property, the powers to renationalise Scottish railways and new land purchase powers – proposals the Tories are likely to resist.
A former colleague of Brown who now backs a yes vote, Bob Thomson, a former Scottish Labour party chairman, said many party members and Labour voters believed Westminster was incapable of implementing the socially just policies Scottish voters wanted.
"Many Labour voters and members are realising that the Scottish parliament offers a much better way of making sure that the wealth of Scotland works for the people of Scotland than Westminster ever has," he said.
"Labour voters also see that the powers offered by the no campaign parties don't go far enough in being able to transform Holyrood from a parliament able to mitigate harmful UK government policies to one that can create a fairer, prosperous and more just society."
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