Former Scottish Liberal Democrat finance spokesman Jeremy Purvis will lead a new group calling for more powers for Scotland short of independence.

Devo Plus, a cross-party and non-party group, will be launched next week to promote "a new and sustainable financial relationship between the Scottish Parliament and Westminster".

The group was formed following months of discussions between participants from across the political spectrum.

Devo Plus has been set up by independent, non-party thinktank Reform Scotland, whose chairman is the businessman Ben Thomson, and will be led by Mr Purvis.

He was one three high profile former MSPs to join Reform Scotland after losing his Midlothian seat to the SNP in the May 2011 election.

Former Scottish Labour leader Wendy Alexander and former Scottish Conservative finance spokesman Derek Brownlee also joined the thinktank.

Mr Purvis said: "Devo Plus is a well thought-out proposal which would provide a sustainable future for Scotland within the UK. It is not a compromise between the two extremes of independence and the status quo - it is the best option for Scotland, and it is the answer to the demands of the people of Scotland for more powers short of independence.

"Our objective is to see the creation of a system in which the Scottish Parliament, as far as possible, raises the money that it spends. That is the principle that underpins Devo Plus and it is the principle on which this group is based.

"Scotland cannot fulfil its potential while it is dependent on Westminster to raise taxes for it. Devo Plus will make Holyrood and Westminster accountable and responsible for raising what each Parliament spends in Scotland. That is fair, and right.

"Crucially, Devo Plus is not Devo Max. The term 'Devo Max' has been used, wrongly, as an umbrella under which all fiscal solutions from Calman to independence can hide, when in fact it is a very specific proposal by the SNP, which would lead to constant friction. Fundamentally, it does not address accountability issues either.

"Many people in Scotland, from figures in the opposition parties to groups such as The Future of Scotland, have been asking for an answer to the question of how to meet the aspirations of the majority of Scots who want more powers than the Scotland Bill offers without wanting independence. This is the basis of the answer."