Gordon Brown's promise of more devolved powers if Scotland voted No in the 2014 independence referendum was motivated by "ego", a former Labour MP has claimed.

Tam Dalyell, who served as an MP in West Lothian from 1962 to 2005, made the comment in an interview with STV News political editor Bernard Ponsonby.

When asked if a passage about the former Prime Minister in his forthcoming book The Question of Scotland: Devolution and After implied the Vow was done for ego, Dalyell said "yes".

He added he was "very angry about it".

In the book, the former Father of the House writes: "But much more serious was the last minute intervention of Gordon Brown with the Vow.

"Self-appointed and wanting a role in which he would be seen to turn the tide in favour of a No vote, Brown gave hostages to fortune, conceding hitherto uncovenanted powers for the Scottish Parliament which, I fear, will lead to recriminations about the politics of betrayal."

Dalyell also called the then-leaders of the Conservatives, Labour and Liberal Democrats "crazy" for allowing Brown to be seen as their spokesman.

The veteran Labour figure also cast doubt on former Labour leader John Smith's commitment to devolution.

Smith has been widely regarded as as one of the leading proponents of legislative devolution.

The former Monklands East MP pushed the legislation for a referendum to create a Scottish Assembly through the House of Commons in the 1970s and remarked it was the "settled will of the Scottish people".

Dalyell questioned Smith's commitment to constitutional change in his earlier years.

He writes: "The truth of what John Smith really felt about devolution will never be known for certain.

"My clear memory is that when, in 1974, he was the parliamentary under secretary of state for energy and then justifiably promoted to be minister of state, working under Tony Benn, as secretary of state for energy, he would point out that the North Sea oil industry depended on not only workers and support from Aberdeen but also from Teesside, Hull and Lowestoft.

"He was scathing about the SNP slogan 'It's Scotland's oil'. I don't claim that he was against an assembly in Edinburgh. I do claim that Smith had not thought very much about the issue."

Dalyell, a lifelong anti-devolutionist, clashed in the House of Commons with Smith over the issue for many years.