NICOLA Sturgeon has accused David Cameron and George Osborne of insulting the intelligence of voters ahead of next month’s EU referendum, and warned that the UK Government’s Project Fear rhetoric could backfire massively.

Sturgeon made the comments yesterday as she joined with Plaid Cymru’s Leanne Wood and Green Party MP Caroline Lucas to launch “the positive case for EU membership”.

The First Minister’s plea for a more upbeat campaign seems to have been rejected by the Prime Minister, who will today warn that the cost of family holidays to Europe will rise by an average of £230 if the UK leaves the EU.

Cameron is expected to say that: “All the evidence points to the value of the pound falling after a vote to leave the EU. A weaker pound means people’s hard-earned savings won’t go as far on holidays overseas.

“The choice facing the British people on June 23 is increasingly clear: the certainty and economic security of remaining in the EU, or a leap in the dark that would raise prices – including the cost of a family holiday.”

Cameron’s warning is based on the analysis released by the Treasury yesterday.

The First Minister said that analysis, which claimed Brexit would result in 820,000 jobs losses and house prices falling 18 per cent, was “overblown” and would harm the campaign. “I think you only have to look at the Scottish referendum to know that that kind of fear-based campaigning, that starts to insult people’s intelligence, can have a negative effect,” she said.

“I would much rather we were campaigning positively. I think in Scotland certainly, we have got lots of experience of Treasury reports during referendum campaigns, and I think people have got savvy – to be able to see through some of the overblown claims.

“Of course, there will be an economic impact, short, medium, and long-term, if there was a vote to leave the EU. But I’m much more interested in the positive reasons to stay in the EU,”

In their joint statement, Sturgeon, Wood and Lucas said that the EU, while not perfect, still came with significant benefits, pointing to rights around working and health and safety.

In a referendum campaign that has been largely dominated by men, the joint appearance of the three high-profile female politicians was notable, and their statement specifically made reference to why Brussels was “good for women.”

“From maternity and paternity leave for parents, workplace rights during pregnancy, to rules protecting against harassment and unequal

treatment, women in Britain benefit from the EU. Crucially, these rules – which span the continent – help halt a race to the bottom of firms trying to find the least protected workforce where workers enjoy the fewest rights.”

They also defended the the right to freedom of movement, which they claimed was “often the focus of attack by other parties”.

“Being a part of the EU is good for our young people, allowing them the freedom to explore the continent, learning as they go and in turn returning home with a wealth of knowledge and perspectives that creates a society that is truly outward-looking.”

All three women committed to spending the next four weeks making the argument for the UK to stay in Europe, but that call for a positive case has been rejected by the Prime Minister.

It came as a new poll suggested support for staying in the EU had grown in recent weeks.

The ICM poll for the Scotsman said 54 percent of Scots wanted to stay and 32 percent backed Brexit, with 14 per cent don’t knows.

In March, an ICM poll for the newspaper had Remain on 50 per cent of the vote, and Leave on 35 per cent.

There has seemingly been only a little movement in the don’t knows, which were 15 per cent three months ago.