DAVID Cameron must campaign positively for the UK to say in the EU or risk Britain's exit from the Brussels bloc, Nicola Sturgeon has warned.
In her starkest comments yet on the UK's future in the EU, she urged the Prime Minister to focus on "big, in-principle" arguments such as jobs and investment, rather than the reforms he hopes to agree with other EU leaders.
Ms Sturgeon said she hoped all four UK nations would vote to stay in the EU but voiced "increasing concern" at the prospect of an referendum in June, which she claimed would not allow sufficient time to engage voters in the debate.
She also expressed fears the In campaign could be overtaken by the Out side if it made some of the same mistakes as Better Together, the official No body in the 2014 independence referendum.
Speaking at a press briefing in Edinburgh Ms Sturgeon said Mr Cameron would be guilty of a "failure of leadership" if he did not "get out there" and campaign positively.
At the weekend, Mr Cameron said he favoured a June referendum if he is able to secure a series of reforms, including limits to migrants' welfare entitlements, at a meeting of the European Council next month.
The date would mean the In/Out debate taking place at the same time as the campaign for the Holyrood election on May 5.
The First Minister has repeatedly said the EU referendum could trigger a second independent referendum if Scotland votes In but the UK as a whole decides to leave.
However, she appears increasingly keen to avoid the scenario.
Pledging to  campaign "for Scotland and, indeed, the UK" to stay in the EU, she said: "I fear that by focussing on the narrow issues of the renegotiation the UK government is in danger of selling the pass on the big economic and social arguments for staying in the EU and leaving too little time for these big issues to be engaged with.
"I think David Cameron should make clear now that when the renegotiations are dealt with he will focus on these big, in principle arguments, on jobs, investment, on the impact on our society and culture of staying in the EU.
"Not to do so would risk jobs in Scotland and across the UK.
"I'll be making the case for our EU membership in Scotland and I hope the Prime Minister quickly stops giving ground to the leave campaign and gets out there are starts making the positive case.
"To do otherwise would be a failure of leadership."
Ms Sturgeon welcomed the appointment of Kevin Pringle, Alex Salmond former chief spin doctor, to the pro-EU "Stronger In" campaign group.
She added: "I'm reasonably confident Scotland will vote to stay in the EU.
"If you'd asked me six months ago I'd have said the same about the UK.
"I'm less sure about that as time moves on.
"I hope that still will be the case but the polls are starting to look less than comfortable.
"If you think about the Scottish referendum the two campaigns started off quite far apart and ended up fairly close.
"Here they are starting much, much closer and my fear is that if the In campaign runs the same kind of campaign as the No campaign in the Scottish referendum they could find themselves overtaken."
In a wide-ranging Q&A session, the First Minister threw her weight behind the Scottish Greens' bid to be treated as a major party by broadcasters in the run-up to the Holyrood poll.
The BBC and STV have provisionally classified the Greens as a smaller party, a move that would limit their airtime and party election broadcasts and not guarantee them a place in leaders' debates.
Responding to a series of inquiries into the financial affairs of SNP MPs, she said her party's procedures for vetting candidates should remain "under review".