GORDON Brown has launched a thinly-veiled attack on the Conservative Government’s negative campaigning as he called for a European Union fund to be set up to help parts of the UK which were facing the strain of increased immigration.

Less than 48 hours after Nicola Sturgeon urged George Osborne to steer away from “fear-based campaigning” and urged the Chancellor to enthuse rather than scare people, the former Labour Prime Minister stressed how warnings of "negative consequences" would not be enough to win on June 23, drawing a parallel with the Scottish independence referendum.

The Herald: Passion, positivity and patriotism: Gordon Brown says Brexit is not British

No 10 has brushed aside such concerns, insisting that while it is right and proper to warn of the dangers of Brexit, it is also promoting strongly the positive arguments for staying in the EU.

In a speech to the European Parliament, Mr Brown said: "In a few days' time the focus of the referendum will shift from the current battle for the hearts and minds of Britain's 11 million Conservatives to an even larger group - Britain's 14m voters, nine million of them Labour, who are not right-of centre - and to the danger that many of them will not vote Remain but simply remain at home.

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"While more instinctively pro-European, this group's concerns are not the same as the Conservatives. They do not think the status quo is to their benefit; they want to know how their lives can improve and they need to hear a positive message of how Europe can deliver for them in the future.”

The Herald: Gordon Brown (REUTERS/Neil Hall)

Mr Brown went on: "To win in the Scottish referendum we had to do much more than elaborate the negative consequences from the break-up of Britain. We had to set out a positive reform agenda, which eventually led to a new constitutional settlement.”

He added: "Fortunately, there is an evolving agenda for the 2017 UK presidency of the European Union, which can make a reformed Europe work better for Britain and show how Britain can lead in Europe."

The former MP, who now concentrates most of his time on campaigning for charitable causes, said that if the UK stayed in the EU, it could press forward a six-point reform plan when it next held the rotating presidency in 2017.

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Among his suggested changes were a "migration challenges and support fund - a European solidarity fund - that helps communities in which healthcare, schools and public services are under pressure because of sharp population changes".

The Herald: Gordon Brown

Britain should, he argued, also propose "stronger measures at the European level" to protect workers "undercut by exploitative employers in other European countries or operating underground in the UK".

This, he said, should argue for a large slice of up to 16 per cent of a £242bn infrastructure initiative "to help our hard-pressed industrial communities, hit by closures and restructuring", for "more sophisticated cross-border intelligence-sharing" and the creation of a "modern Marshall Plan" to deal with conflict in the Middle East and Africa.

London, explained Mr Brown, should also lead calls for "a more comprehensive European strategy using our presidency to blacklist, sanction and, where necessary, impose withholding taxes on the havens that have become treasure islands for the tax-avoiding few".

The former PM stressed: "Around these priorities we can construct a bigger pro-European majority and begin to fashion a British consensus on the future of Europe.”

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He claimed the Leave campaign would argue that a Britain which gained only grudging concessions from the EU before the vote would be treated harshly after it. “The opposite is true,” declared the Scot, “with a clear domestic mandate, we will be in a far stronger position to shape Europe's future.

The Herald:

"The positive agenda I propose is not only essential to convince Labour and progressive voters to turn out on June 23 but it is also the correct way forward; with Britain discovering a post-imperial role that makes us proud to be in the vanguard of the next stage of Europe's development. In short, we should be leading Europe, not leaving it."

Meantime, his former cabinet colleague, Lord Darling, urged Jeremy Corbyn to step up his own involvement in the Remain campaign.

The former chancellor said the Labour leader had a "big role to play" in the debate ahead of the June 23 vote. While the peer said Mr Corbyn was playing his part in the campaign but added: "I hope he will be more involved" as the referendum date drew nearer.

The Herald: Alistair Darling said Brexit would be 'disastrous' for the UK

He told BBC Radio 4's Today programme: "The leader of any main political party in this country, and the leader of the opposition, has a big role to play and I hope that he does more. However, this is a broad-based campaign of all parties and people of no parties.

"The key thing we have got to keep in the front of our mind is we are taking this massive decision, there is a huge amount of risk if we leave."

The Labour In campaign is being led by former cabinet minister Alan Johnson rather than Mr Corbyn, who has a history of Euroscepticism.

Lord Darling also noted how the respected economic think-tank, the Institute for Fiscal Studies, had become the latest independent group to warn about the economic cost of Brexit. It has warned that the short-term economic shock of leaving the EU could see the era of austerity continue for an extra two years with spending cuts and tax rises running into billions of pounds to fill the financial black hole.

"We have now got a wide range of estimates from a number of independent analysts and they all point in the same direction and that is if we were to leave there would be a hit on the economy,” said Lord Darling.

The Herald: Leader of the Better Together campaign, Alistair Darling, speaks to the press at the campaign headquarters at the Marriott Hotel, Glasgow, on on September 19, 2014 - the day after the independence referendum.

"That would hit jobs, it would also hit the amount of money we have got to spend on services like health and education.

"You can't set that aside. The important judgment we have to reach in a month's time is what do we think would happen if we remove ourselves from a market of 500 million people?

"It is fanciful to believe that somehow you could leave that single market and there wouldn't be any damage whatsoever. You will be taking a huge risk if you do this," he added.

Earlier, the IFS rejected claims that it was acting as the EU's "propaganda arm" by issuing its stark warning about the potential impact of Brexit.

David Cameron - whose policies have often been savaged by the think-tank – was keen to point out on this occasion that the IFS was "always held out as the independent gold standard".

The Herald: David Cameron attacked Penny Mordaunt's claims that Britain had no veto over Turkish accession to the  EU

"What they are saying about the £350m claim and what they are saying about the effect upon our economy of Brexit, that is very, very powerful and it backs up what the Treasury and others have been saying," the PM said as he arrived in Japan for the G7 summit.

The think-tank’s report said a vote to Leave could see public finances take a £20bn to £40bn hit in 2019/20, if gross domestic product were 2.1 per cent to 3.5 per cent lower over the period, as predicted by another think-tank, the National Institute of Economic and Social Research.

Paul Johnson, the IFS’s director and an author of the report, said: "Getting to budget balance from there, as the Government desires, would require an additional year or two of austerity at current rates of spending cuts."

The think-tank said Britain could use its contribution to the EU - estimated at £8bn a year - to help shore up its finances if it voted for Brexit. But it said this could be overshadowed by the negative impact on the UK economy, with a 0.6 per cent fall in national income offsetting the benefits.

It also dismissed claims from the Leave camp that the UK would have an extra £350m a week to spend if it headed for the European exit door, while the saving from leaving the EU would be halved if it followed Norway and joined the European Economic Area.

The Herald: LEAVE: Gisela Stewart, who fronts the 'Vote Leave' campaign in Worcester.

However, Vote Leave dismissed the IFS as a "paid-up propaganda arm of the European Commission" which could suffer a financial hit from Brexit because it benefited from EU funds.

"The IFS is not a neutral organisation. It would face an £800,000 deficit if we vote Leave," the campaign insisted.

In 2014, 11 per cent of the think-tank's research funding came from the EU and it has received more than £5.6m from European Commission sources since 2009, Vote Leave said.

But Mr Johnson pointed out his organisation received European funding for some of its "academic work" as did other institutions outside the EU.

"For the last 30 years, the IFS has built its reputation on the independence and integrity of our work and actually there is no sum of money from anywhere in the world which would influence what we said because, if it did, then the point of the IFS and the reasons ... that we are listened to after budgets and so on would simply be lost," he said.

The IFS report - funded by the Economic and Social Research Council's UK in a Changing Europe scheme - said a vote to Leave would increase economic uncertainty in the short term, ramp up the cost of trade and make the UK less attractive to foreign investment.

It said these pressures could see borrowing come in more than £20bn higher in 2019, if national income fell in line with NIESR's prediction of a 2.1 per cent drop over that period.

The Herald: Chancellor George Osborne said house prices would take a hit of as much as 18% if Britain leaves the EU

It found that the Government would have to find the equivalent of £5bn of public spending cuts, £5bn of savings from social security spending and roll out £5bn of tax rises if it wanted to balance the books by 2019/20.

Mr Osborne has pledged to return the UK to a surplus by 2020 with the Office for Budget Responsibility forecasting that the UK would have a budget surplus of £10.4bn in 2019/20 and £11 billion the year after.

But Patrick Minford, co-chairman of Economists for Brexit, said: "The IFS analysis acknowledges that the unilateral free trade approach recommended by Economists For Brexit would be the best option for the UK following an exit from the EU.

"The IFS comments that it is 'politically difficult' to embark on this WTO (World Trade Organisation) path. Yet this is entirely irrelevant for what is a purely economic argument."

However, Mr Johnson said the kind of economy envisaged by Prof Minford would involve "very substantial" costs during the transition process, with the loss of much of the UK's manufacturing industry.

Brexit-backing Tory former cabinet minister John Redwood noted: “The IFS are part of this cosy Establishment which desperately wants to keep us in the European Union."