THE pro-UK parties' late pledge to deliver more powers for Holyrood had "zilch" impact on the result of the referendum, a former SNP leader has claimed.

Gordon Wilson said the Yes campaign lost last September because it failed to persuade people of the economic argument for independence.

His views put him odds with former SNP leader Alex Salmond, who has said the so-called 'vow,' made by the Better Together parties days before the vote, had a decisive effect.

Mr Salmond will assess the campaign in his book, The Dream Shall Never Die, due to be published later this month.

Asked what impact the vow made, Mr Wilson said: "Zilch. I think it's a myth.

"I've never found people pay too much attention to constitutional proposals, they tend to focus on how they would do economically.

"It was not Better Together that won, it was 'better off' that won."

He added: "I've a different view on that from Alex. He may well be right, that's as far as my concession would go."

Mr Wilson was speaking at the launch of a new 'strategy for independence,' issued by his Options for Scotland think tank.

It said the Yes campaign's biggest "weak point" was its failure to spell out an economic vision for the next 20 years.

Mr Wilson said the SNP should only press for a fresh referendum at a point when opinion polls have indicated at least 55 per support for independence for a sustained period.

He said the timescale for a second vote "lies between five to 20 years".

He called on the SNP to create a special research and communications unit to campaign for independence separately from from parliamentary party, which he said was too focused on elections.

The former MP, who led the Nationalists throughout the 1980s, played down the prospect of an EU referendum triggering a vote on independence, saying England was unlikely to back withdrawal.

Mr Wilson said Labour could become part of a pro-independence alliance if the party suffers a resounding defeat in May's General Election and has to reform afterwards.