Britain's departure from the European Union could see the country descend into economic "protectionism" that would hurt business, warned Phil Couchman, UK head of the German logistics giant DHL's 'Express' business.
Speaking to the Huffington Post UK, Couchman said: "If something went dramatically wrong with the trading relationships between the UK and the EU, it would affect us and a lot of businesses."
"If a parting regressed into protectionism towards the rest of Europe, then that would be a bad thing and a backward step."
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Couchman praised the European Union's single market for offering a "greater domestic market" for businesses.
He added: "A greater domestic market is easiest to do business in. We see all manner of products doing quite well in the neighbouring countries. When businesses do start exporting, the person they turn to first is Europe, the European Union and then perhaps the English-speaking countries."
The DHL Express boss' comments come after Nissan urged the UK to stay in the European Union, in concerns about the upcoming referendum in 2017.
Toshiyuki Shiga, Nissan's chief operating officer, said: “The UK is part of the European Union — that’s very important. From the foreign investor’s point of view, I hope that the UK will remain an EU member.”
“A lot of regulations are under the EU. If the UK, after departing from the EU, made unique regulations, unique standards, that would become an obstacle," he said.
“If the EU side put import duties on the UK that would be a big obstacle. It depends what happens after leaving," he added.
The Ukip leader and MEP is the most famous 'outer'. After his party took over a 100 council seats in May's local election's Nigel Farage is hoping to win the 2014 European elections and then gain MPs in Westminster in 2015. He has confirmed he will seek a parliamentary seat himself.
Margaret Thatcher's former chancellor and a true 'Tory grandee' revealed in The Times that if and when there is a referendum "I shall be voting out". He also stuck the boot into the David Cameron by saying the prime minister's attempts to renegotiate the terms of the UK's relationship with the EU would be "inconsequential".
There are quite a few Conservative MPs who would like to wave goodbye to Brussels. Ken Clarke has said the figure is as low as 30 despite the strong eurosceptic feeling on the backbenches. However the exact number is not clear. Mid-Bedforshire MP Nadine Dorries, who remains suspended from the Conservative Party, is currently talk tof the eurosceptic town amid rumours she may defect to Ukip. Other backbench Brexiters include Bill Cash, Douglas Carswell, Peter Bone and Philip Davies and former defence minister Sir Gerald Howarth.
Most of the anti-EU focus is on the Tory benches. But there are more than a handful of Labour MPs would would like to quit Brussels as well. Eurosceptics include Frank Field, Kate Hoey, Austin Mitchell, and Gisela Stuart. Stuart has argued the status quo is "not sustainable" and Britain should leave.
Rupert Murdoch has warned that the EU will "sink" the UK. The News International and boss caused a stir when he met Nigel Farage for dinner in London recently and said the Ukip leader was "reflecting opinion" with his anti-EU views. In November 2010 Richard Desmond’s Daily Express became the first UK newspaper actively to call for Britain to leave the EU, launching a ‘Get Britain Out’ campaign
Of course no campaign is complete without a bit of star power. The pro-EU camp have Eddie Izzard, who do the Brexiters have? Joan Collins, a 'patron' of Ukip, wants the UK to leave. "The EU, controlled from Brussels, cares only about itself," she said in March.
Most business leaders do indeed seem content with what Lawson called the "warm embrace of the European single market", but there are a few dissenters. Private equity guys Jon Moulton and Edmund Truell are two and Next boss and Tory peer Simon Wolfson has said: "Britain should stay in Europe, but only on the right terms".
There are a number of loud voices whinnying on the sidelines to say "neigh" to the EU notably Melanie Phillips, Richard Littlejohn, Tom Utley, Simon Heffer. Basically the Daily Mail stable.
Several high-profile politicians appear to be on the verge of calling for the UK to exit the EU - but just are not there yet. Former defence secretary Liam Fox - pictured here with a big gun - has said "life outside the EU holds no terror" should David Cameron's hopes of negotiating a new treaty fail. Education secretary Michael Gove is said to have told friends the UK has "nothing to be scared of" by leaving Europe. And many other eurosceptic cabinet ministers, including Iain Duncan Smith and Owen Paterson are likely to share that view.