Pair claim that party will go further than ‘the vow’ made during referendum campaign promising more powers for Scottish parliament

Jim Murphy and Gordon Brown will on Monday pledge that a Labour government would radically extend Scotland’s powers over welfare, following speculation that Brown is to take a prominent role in his party’s general election campaign in the hope of repeating the success of his last-minute intervention in the independence referendum.

Murphy, the new Scottish Labour leader, and Brown will share a platform in Edinburgh to announce a “distinctive Labour change”. This, they say, goes further than “the vow” of more powers to the Scottish parliament, brokered by Brown and signed by all three party leaders in the days before the referendum vote, as well as the all-party Smith commission which fast-tracked agreement on those powers.

While Smith recommended devolving £3bn of welfare powers, including the housing elements of universal credit, and the power to create new benefits in devolved areas, and top up UK payments where affordable, Murphy and Brown will pledge to extend these powers to benefits in non-devolved areas, including child benefit and state pensions, as well as fully devolving housing benefit, worth £1.8bn.

Brown will say: “We will go further by ensuring that the final say on benefit levels remains in Scotland by giving the Scottish parliament a wider power to top up UK benefits. This will ensure that Scotland is protected from Tory welfare cuts – there could never be another bedroom tax in Scotland – and from benefit cuts caused by a fall in Scottish funding due to, for example, the collapse in the oil price, the inevitable consequence of the nationalists plans for full fiscal autonomy.”

Describing the delivery of the vow as “a starting point not an end point” for Scottish Labour, Murphy will add: “A Labour approach to powers, and to the use of powers, will reflect our different values and different ambitions for Scotland. We have different values from the Tories on welfare and different values from the nationalists on redistribution.”

He will also say that Labour plans a separate Scottish manifesto.

Brown is standing down from his seat of Kirkcaldy and Cowdenbeath but has promised to “do everything I can” to secure Ed Miliband’s election as prime minister. With Labour trailing the SNP in the polls.

Some believe Brown could reach out to disaffected Labour voters in the same way he did last September, when he was credited with winning back wavering no voters.