Quitting the EU would cause shop prices to rocket and prove ‘catastrophic’ for millions of families, four of Britain’s most successful high street bosses warn today.

In a dramatic intervention in the EU referendum debate, the former chiefs of Tesco, Sainsbury’s, Marks & Spencer and B&Q say leaving the EU would have a devastating effect on the economy.

And they dismiss one of the key claims put forward by ‘Leave’ campaign leaders Boris Johnson and Michael Gove – that we would be better off without EU regulation – as ‘nonsense’.

Sir Terry Leahy (left). He trebled Tesco's value to £30bn during his 14-year reign as chief executive from 1997-2011. Sir Ian Cheshire (right) was chief executive of B&Q owner Kingfisher from 2008-2015, doubling its value to £8bn

They also argue that an ‘Out’ vote could lead to:

A spike in inflation;

Job losses;

A plunging pound.

The retail experts say the French could even start a tit-for-tat trade war in revenge, banning British lamb if we voted to sever ties with Brussels on June 23.

In an article in today’s Mail on Sunday, the former high street bosses – Sir Terry Leahy of Tesco, Marc Bolland of M&S, Justin King of Sainsbury’s and Sir Ian Cheshire of B&Q owner Kingfisher – say: ‘We believe an exit could be catastrophic for the consumer recovery on which so much of our economic stability depends.

‘It is impossible to see how there could be an exit without an impact on prices and inflation. The unintended consequences of a Leave vote and the uncertainty it would create would be a massive shock to the system’.

Justin King: Former head of M&S's food division, he became chief exec of J Sainsbury in 2004, where he remained for a decade, boosting group sales from £15bn a year to £25bn

Marc Bolland: After turning ailing Morrisons in his three years as chief executive, Bolland joined M&S in 2010, and left last month. Aged 57, he is also a director of Coca-Cola

They say that a victory for the ‘Leave’ campaign would force Britain to seek new trade deals with other countries – who were likely to ‘exploit this renegotiation to their benefit.’

They say the French could be particularly problematic, warning: ‘It’s difficult to imagine that French farmers will continue to allow British lamb to be freely imported.’

Although they don’t mention Johnson and Gove by name, they demolish their argument that Britain would be better off without EU regulations. In fact it would make it harder for UK firms to sell goods to Europe, they say.

The retailers add: ‘The much-cited suggestion that we will be free of the apparent constraints of over-regulation if we leave Europe is nonsense. We need regulation to protect consumers and, if we want to continue to trade with Europe, the rules still apply.

‘If we left, there is the risk that Westminster would continue to build additional regulation on top of the European laws, making it more onerous rather than less.’

The shop bosses’ intervention was last night welcomed by David Cameron, who told The Mail on Sunday: ‘This is a stark warning from our most successful retailers about the risks Britain faces if we take a leap in the dark and leave the EU.

‘They are absolutely clear that millions of families will face higher prices in the shops’.

The retail chiefs’ warning is echoed today by former Labour Chancellor Alistair Darling, who says Brexit could leave people around £1,800 worse off per year each – or nearly £150,000 over a lifetime.

The UK would be left ‘permanently poorer,’ he writes in an article for The Mail on Sunday. ‘The cost will fall most harshly on our children and grandchildren every year of their lives.’

Between them, the four supermarket bosses employed 750,000 staff and were responsible for nearly £100 billion in annual sales.

Mr Cameron has been buoyed by two recent polls giving his ‘Remain’ camp a double-digit lead over Mr Johnson’s ‘Leave’

Their views were echoed last night by a fifth former retail giant, ex-Waitrose managing director Mark Price, now a Government Trade Minister, who said: ‘Leaving the EU will see further pressure on the pound, which will mean higher prices.’

Tomorrow, the ‘Leave’ campaign will launch a provocative advertising drive designed to exploit immigration fears over the possibility of Turkey joining the EU. A nationwide poster campaign will show dozens of footsteps walking through an open British passport.

Mr Cameron has been buoyed by two recent polls giving his ‘Remain’ camp a double-digit lead over Mr Johnson’s ‘Leave’.

But the former London Mayor hopes to close the gap when the pre-referendum purdah starts on Thursday, banning Ministers from using Whitehall to promote the ‘Remain’ argument.

The ‘blue on blue’ war of words between Tories across the divide has become increasingly bitter. Yesterday, Mr Gove’s close ally Dominic Cummings, the campaign director of Vote Leave, ridiculed George Osborne’s claim that house prices would plummet as a result of Brexit.

The Chancellor was using Treasury analysis that would be banned during purdah.

Mr Cummings posted a message on Twitter saying: ‘Credibility of Whitehall forecasts deeper in toilet with HMT’s [Her Majesty’s Treasury] balls on house prices & Osborne destroying own credibility & leadership hopes’.

A spokesman for Vote Leave, responding to the retail chiefs’ article, said: ‘The EU is good for the bosses and for the bankers. It isn’t good for the public who have to pay the taxes that go to the EU instead of to our NHS and it isn’t good for small businesses.

'As independent experts have found, the EU pushes up the prices in our supermarkets because of its protectionist policies.’

FOUR GIANTS OF UK RETAIL BREAK SILENCE WITH DEVASTATING VISION OF AN OUT VOTE 'We have had the privilege of leading some of Britain’s largest and most successful retailers. Over the past 20 years, retail has been through a phenomenal transformation and remains one of the most dynamic and innovative industries in the UK. Consumers have never had such a large range of choice and quality. They can shop 24 hours a day, either in stores or online, at prices more affordable than ever. This has all been achieved with Britain as part of the European Union. Like the Leave campaigners, we believe Britain is a truly world-class country. But unlike them, we believe an exit could be catastrophic for the consumer recovery on which so much of our economic stability depends. It is impossible for us to see how there could be an exit without an impact on prices and inflation, the strong relationships we’ve built with our EU supplier partners, and the broader innovation and digital agenda. The unintended consequences of a Leave vote and the uncertainty it would create would be a massive shock to the system. It would probably mean further depreciation of the pound, driving up the price of imported goods for consumers. In the UK we have strong and sophisticated supply chain relationships across Europe, integrated in a way they never were in the past. At the moment there are no barriers to trade within the EU. In trading with the rest of the world, all sorts of rules and tariffs get in the way. A vote to exit would necessitate a complete renegotiation of our trading arrangements, which can only be of detriment to UK consumers. We can also expect our trading partners to exploit this renegotiation to their benefit. It’s difficult to imagine French farmers will continue to allow British lamb to be freely imported. This leads to questions over the future of British agriculture as well as food manufacturing – an industry in which we are net exporters – and therefore the ultimate impact on jobs. There is no guarantee we can renegotiate quickly and efficiently enough to deal with some of these issues. As large retailers, our experience over many years is that scale gets you a better deal and being under time pressure is never helpful. British retail’s advancement over the next ten years is heavily reliant on investment in digital technology. The EU’s recently agreed Digital Single Market strategy will open up opportunities for business and consumers across Europe, making the single market fit for the digital age. Britain is the digital hub of Europe and has led the way in shaping the digital economy. Indeed, this country is the e-commerce capital of Europe, with a market share of over one third. We have the expertise to continue to lead and it would be a massive missed opportunity to leave the EU now and not be part of the broader revolution. Finally, there is the issue of regulation. The much-cited suggestion that we will be free of the apparent constraints of over-regulation if we leave Europe is nonsense. We need regulation to protect consumers and, if we want to continue to trade with Europe, the rules still apply. If we left, there is the risk that Westminster would continue to build additional regulation on top of the European laws, making it more onerous rather than less. So it makes much more sense to have a seat at the table to shape future regulatory change rather than simply be bound by it. There is no doubt this is a fundamental decision for the British people. While we are not advocates of scaremongering, it is just good business to understand the risks before reaching a conclusion in this complex debate. We have a responsibility to help inform the consumers we have served for many years. While the EU is by no means perfect, exit would hit consumers the hardest. For that reason we will be voting to stay and continue to play our part in the successful and growing Europe we all want to see.' Sir Terry Leahy, Justin King, Marc Bolland and Sir Ian Cheshire Advertisement

Brexit’s big idea is a total Turkey, says former Labour chancellor ALISTAIR DARLING

Alistair Darling: 'Brexit’s big idea is a total Turkey'

If evidence is needed that Vote Leave campaigners have abandoned the economic argument, take a look at their fearmongering over new countries joining the EU. Their wild predictions are designed to deceive rather than inform.

Under current proposals, Turkey won’t join the EU in the foreseeable future. If this ever became a realistic prospect, the UK government could veto it, as could all EU countries.

The idea that Turkey and others are on the brink of joining is such a far-fetched notion that even Boris Johnson has said it is ‘simply not on the cards’.

So why is the Leave campaign reaching for the Ukip playbook? Because they cannot win an argument that Britain’s economy will prosper outside Europe.

Analysis by the Treasury, the International Monetary Fund (IMF) and the Organisation for Economic Co-operation all underline the scale of the risk we face. Overwhelming evidence shows that if we vote leave, the UK would be permanently poorer. The case is unanswerable.

Assuming we were to follow Vote Leave’s policy of negotiating a new free-trade agreement, the annual cost of leaving to the economy would be the equivalent of £1,800 per person per year. This cost will fall most harshly on our children and grandchildren.

And it’s a cost they will face every year of their lives. For those born between 2012 and 2014 the cost over their lifetime would be a staggering £145,800. Not a land of opportunity outside, but the next generation weaker and worse off.

The Governor of the Bank of England and the IMF have both said that if we leave, the result could be ‘recession’ for the British economy. The prospect sends shivers down my spine. I was there last time and I don’t want our country to revisit the experience.

If there is one thing I know about, it is how it feels when a country faces potential financial ruin. As Chancellor in 2008, I saw the catastrophic effects of a breakdown in confidence and deep uncertainty after the banking crash. I saw confidence drain and jobs threatened, forcing everyone – Government, businesses and families – to take dramatic steps to keep the economy going.

Historical evidence and recent experience show that, when we suffer recession, then insolvencies, repossessions unemployment – particularly among young people – all soar. Between 2007 and 2009, insolvencies rose more than 60 per cent, repossessions almost doubled and the number of businesses being set up collapsed.

New 'Out' poster: Vote Leave’s provocative claim that Turkey is on the brink of joining the EU is dismissed by Alistair Darling as ‘fearmongering’

Do we want to go through such pain again, with working people’s life chances and livelihoods under threat just as they begin to recover? Never again do I want to see people queuing to take their life savings out of cash machines or carrying boxes out of their workplaces. But that is the reality of the Vote Leave offer.

Vote Leave wants Britain to leave the EU’s single market, which was the reason we joined in the first place to pool our sovereignty and reap the benefits of having an equal part of the world’s largest free-trade area of 500 million people.

Within the single market we trade goods and services freely and set the terms of doing business. This brings £250 billion of additional trade, investment, three million jobs and lower prices.

Given those benefits, it is no wonder a majority of businesses large and small want us to stay. If we leave, we will be erecting barriers to trade that would hit half our exports. Where is the sense in that? You cannot walk out of the world’s largest free-trade zone one minute and expect all its benefits to fall into your lap the next.

Norway, outside the EU, has access to trade but has no say over the rules it has to play by. It also must accept free movement of people – the very thing the Leave campaign has set itself against. Switzerland has even more limited access, and Canada, which Boris says we should follow, will not have the full access to Europe’s markets that we have today.

What about trade with the rest of the world? There is nothing to stop us selling more right now to the likes of China or India. Germany, which has a highly successful export trade in engineering goods, does very well while still being a major player in the EU.

The single market works. It protects jobs, which in turn generate money for public services such as the NHS. Vote Leave campaigners want to pretend otherwise, but they cannot counter this argument.

That is why they are betting the house on the age-old strategy of blaming immigrants for everything. Yes, we must control borders, and we do, but recession is no answer to pressures on public services.

As we enter the final five weeks of campaigning it is close, but we in the Remain camp can feel confident. People vote with their pockets and we are winning the arguments over pounds and pence.