Gordon Brown makes rather a habit these days of intervening in fraught political debates at the 11th hour. In the final days of the referendum campaign, the former Prime Minister was instrumental in agreeing a timetable for extra powers for Holyrood. He also intervened in the last days of the Labour leadership campaign to warn against voting for Jeremy Corbyn.

And now here he is at it again as the Scotland Bill makes its way through the House of Commons, warning there are just two weeks left to make the changes needed to fully deliver the Smith Commission proposals. Failing to do so, he says, will create a perfect storm that threatens the union.

Mr Brown's concern is that the Smith proposals on welfare have not been fully delivered by the Scotland Bill. In a speech at Glasgow University, he said the Scottish Parliament was promised the clear and unambiguous right to top up welfare benefits without any possibility of the top-ups being vetoed by the UK Government.

In an attempt to deliver that promise, Mr Brown is now supporting an amendment to the bill which would enable the Scottish Government to override welfare changes made by the UK Government if they are prepared to pay for them; the amendment would also remove any suggestion of a UK veto.

In talking of perfect storms and the end of the Union, Mr Brown is using fairly dramatic language to make his point, but what he is calling for is rather less dramatic – indeed, he is pushing in a direction that the Scotland Bill aims to go in the first place. The Smith Commission suggested the Scotland Government should be able to top up benefits, and the Scotland Bill needs to make that happen. But the problem, as Professor Jim Gallagher, the former advisor to the No campaign has pointed out, is that in handing the Scottish Government the power to supplement reserved benefits, there appears to be some doubt about whether this would be short-term only.

It is in the interests of the UK Government to now remove any lingering doubt and ensure that the language of the Scotland Bill supports its original intention to allow the Scottish Government to supplement benefits. Not doing so, as Mr Brown pointed out in his speech, will only prolong the argument over what powers Holyrood does not have rather than moving the debate on to what powers the Scottish Government has and how it will use them.

When agreement is reached, there may be some work to be done on precisely how top-ups could be made to work (for example, the Scottish Government may want the Department of Work and Pensions to deliver the top-ups of their behalf) but in the meantime, there is more room for agreement on the issue than Mr Brown's speech would suggest. The Scottish Secretary David Mundell has said there would be no veto by the UK Government and there is nothing in the suggested amendments for the UK Government to object to. The objective from the start of this process was to allow the Scottish Government, if it wishes to and is willing to pay for it, to offer top-ups – it is now up to all sides to ensure that objective is met.