IAIN Duncan Smith’s Department for Work and Pensions probably reversed support for major devolution of welfare at a last-minute stage in the process, a team of independent experts examining critical post-referendum discussions found.

The Edinburgh University study, published today, on the Smith Commission and the Process of Constitutional Change drew on interviews with politicians who took part in the body. It is among the first academic studies of the work of the commission. It found there were “two narratives” being taken in the Smith Commission to tax and welfare.

The first was that the integrity of UK tax and welfare policies allowed only the limited discretion that emerged in the final report. The second was that “there was serious interest on the commission in extensive tax and welfare devolution, including from Conservative representatives, but days before the deadline the Treasury and DWP became fearful of repercussions on UK policy and insisted that earlier ideas be dropped”.

The academics concluded: “Our research leads us to give greater weight to the second narrative ... At a late stage the DWP appears to have withdrawn support for anything beyond devolution of the housing costs element. Our research did not explicitly confirm, but certainly fits the narrative, of earlier reports of a last-minute intervention by the DWP (and specifically by Secretary of State Iain Duncan Smith) to take things off the table.”

The Smith process was the process of realising “The Vow” – a text signed by anti-independence party leaders David Cameron, Ed Miliband and Nick Clegg that appeared in the Daily Record two days before the referendum. It said that “extensive new powers for the Scottish Parliament will be delivered ... starting on 19th September”.

It was seen as an intervention which stopped thousands more from voting Yes. Yet within weeks Scots were left feeling empty handed.

Despite the demand for powers over child and unemployment benefit, as well as welfare allowances for the sick and disabled to be devolved, only housing benefit including powers over the bedroom tax were devolved to Holyrood.

SNP Westminster work and pensions spokesperson Dr Eilidh Whiteford said: “This briefing from respected academics provides further proof that the DWP’s meddling in the Smith Commission process resulted in vital powers being denied to Scotland. Westminster has shown time and time again that it cannot be trusted to protect our vulnerable and hard working people – the welfare system is in need of reform and the DWP’s unfair sanctions regime is currently responsible for untold misery across the country.

“That is exactly why Scotland needs full powers over welfare, employment and taxation.”

A DWP spokesperson said: “This is unhelpful speculation. The plans for devolution of welfare were agreed by all the main Scottish political parties and the UK government is now making this happen."