THE author of a model for further devolution of powers to Holyrood has claimed it will be vital for the pro-Union parties to unite around an agreed pledge ahead of the independence referendum in autumn next year.

The first of a series of papers to be published by the Institute for Public Policy Research (IPPR), by constitutional expert Alan Trench, is suggesting "devolution more" involving full control over income tax and the assignation of a share of VAT, which he said would help boost fiscal responsibilities to approaching 60% and align spending powers with revenue raising. Mr Trench also argued the pro-Union parties should reach an agreement on a plan to extend devolution ahead of the independence referendum in autumn 2014 if they are to maintain credibility on the issue. He said: "An agreed model has to be on the table if the case for a No vote is to be credible."

Scots LibDem leader Willie Rennie said an agreement on a firm set of proposals would be "challenging" but a contract based on broad principles was possible.

Labour's Sarah Boyack said the IPPR report was a valuable contribution to the debate on further devolution which would inform Labour's internal report on the issue.