A senior figure in the independence movement has called for Holyrood to hold a snap referendum within two years, piling pressure on Nicola Sturgeon to clarify her intentions.

Patrick Harvie, the co-convener of the Scottish Greens, said a second independence vote could be held during an extended Brexit negotiating process, adding that the SNP Government is in “real danger” of missing an opportunity.

Co-leader Maggie Chapman also said that the Scottish Parliament staging its own referendum unilaterally could be a “very useful tool”.

Pamela Nash, chief executive of the pro-UK Scotland in Union, said: "Rather than listening to their SNP masters, the Scottish Green leaders should listen to the majority of people in Scotland, who don't want a divisive second independence referendum - and certainly don't want one before 2021.

"A wildcat Catalan-style referendum would be even more reckless, with no legal basis.”

The pro-independence movement is split over the timing for seeking another referendum on whether Scotland should leave the United Kingdom.

Sturgeon, the leader of the SNP, is cautious and has said she is waiting for clarity on the outcome of Brexit before revealing her next steps.

A number of her political allies back her stance and want her to attempt to secure another pro-independence majority at the 2021 Holyrood election.

However, Harvie has previously said people in the Yes movement are “impatient” and has called on the SNP Government to set out its position “very soon”. He has also used First Minister’s Questions to ask Sturgeon about her plans.

Speaking to the Herald on Sunday at his party’s spring conference in Edinburgh yesterday, Harvie said he could understand Sturgeon’s wish for more detail on Brexit before laying out her indyref2 proposals.

But he said: “I think there’s a real danger in waiting too long on the hope that clarity, which may never come, is just round the corner.

“To pass legislation for a referendum takes some time. If we wait too long, that won’t be doable in this current session of Parliament.”

Asked if he wanted another independence referendum before 2021, he replied: “If this Brexit process is happening, I would like to see it.”

Harvie said the legislative timescale that led to the 2014 referendum showed that another vote can be arranged within the next two years: “If we leave it even a few months longer we will have run out of time.”

He added: “The scrutiny process might not need to be as extensive.”

With Prime Minister Theresa May unable to get parliamentary approval for her draft withdrawal agreement, it is likely she will have to seek another extension to a leave date currently set at April 12th.

She favours a June 30th departure, but reports suggest the EU wants a much longer delay, which has been called “flextension”.

Harvie said: “If that’s what comes to pass, then yes, it is absolutely eminently possible to hold a referendum in that timescale.”

On the pro-independence figures who want to use the 2021 election as the means to get another referendum, he said: “I think there is a real danger that a window of opportunity could be missed.”

Chapman, who has been joint leader of the Scottish Greens for five years, said of the timing of indyref2:

“It might happen sooner than the 2021 election, simply because everybody knows that the UK is not okay.”

She also addressed what might happen in the event of the UK Government refusing to enter into a joint agreement with the Scottish Government on a second referendum.

The 2014 vote took place after both Governments signed the Edinburgh Agreement, which led to Holyrood temporarily having the power to stage a plebiscite.

Asked about Holyrood holding its own consultative referendum on independence if the UK Government played hardball, Chapman said:

“I think that is possible. I think it is something that might actually be a very useful tool for us.”

She added: “If that referendum came back in favour of independence, and the British Government turned round and said ‘no, you can’t have it’, I think that is another mobilising force.”

Scottish Conservative chief whip Maurice Golden said:

“This is a timely reminder that it’s not just the SNP that wants to recklessly break up the UK. The Greens are equally dangerous and selfish in their relentless pursuit of independence.

“Thankfully, a majority of Scots don’t share that opinion, and don’t want another bitter and divisive referendum.”