The Co-Convener of the Scottish Greens, Patrick Harvie, has reaffirmed his support for Scottish independence but moved to put clear water between his party and the SNP ahead of the 2014 referendum.

The Glasgow MSP said Greens’ support for independence “doesn’t begin with national identity,” and hinted that his party could be persuaded to support a ‘devo max’ option, should it prove to be a better vehicle to decentralise economic and political power.

In an interview with Holyrood, Harvie also raised the intriguing prospect of political parties encouraging members to have a free voice in the independence debate, adding that “anyone who’s really honest knows that the constitutional debate in Scotland doesn’t really split down party lines”.

Independence, explained Harvie, is “not a point of principle for me,” adding: “It’s a purely pragmatic thing, and I have very little interest in flags and identity and 300 years of grudge and grievance.” Greens, he said, support independence as the decentralisation of power – something Scotland has done badly since devolution.

Warning that the independence debate has been “very processy” so far, Harvie called on political parties to engage with civic Scotland’s Future of Scotland campaign, which he said has been “mischaracterised as a devo max lobbying group”. He said politicians at all levels should be allowed to say what they think ahead of the referendum, and seek to begin a wider discussion about the future of Scottish society.

Harvie explained the Scottish Greens will “continue to debate both the fundamentals and the specifics” of the issue at the party’s conferences both this year and the next. The party, he added, “may want to refine the policy a bit – particularly if there’s a third option”.

In a dig at the apparent dominance of the SNP leadership in formulating its independence strategy, Harvie explained that his party’s position would be based on a member’s vote. The Greens, he said, have a “weird tradition” of allowing members a say in policy, rather than “a dictatorial system where Alison (Johnstone, Harvie’s fellow Green MSP) and I carve things up in the Holyrood office and then tell the rest of the party what to believe in”.

Harvie criticised the most popular interpretation of ‘devo max’, in which Scotland would share defence and foreign policy with the UK, arguing that “the constitutional politics of it make very little sense”.

He continued: “If Scotland were to take more control over its economy, business regulation and a whole swathe of legislative power, your interest in representing yourself on the world stage is dramatically stronger than it is now – so you would need to take control of your foreign affairs.

“If you take over foreign affairs, is it credible to have a shared defence policy with another country that has separate foreign affairs?” Harvie added that: “The currency issue is a perplexing one, it seems to me there is no right answer at the moment,” he continued. “Either you’re talking about a currency union without a political union to manage it – and that goes for the pound or the euro – or you are talking about something separate.”