BHP Billiton Andrew Mackenzie
BHP Billiton CEO Andrew Mackenzie said Britain should vote to remain in the EU Reuters/Rick Wilking

Andrew Mackenzie, the chief executive of mining giant BHP Billiton, has warned that leaving the European Union could spell the beginning of a decade of damaging economic uncertainty for British business.

Speaking on Monday (18 April), Mackenzie said Brexit would be detrimental to both the EU and Britain, with the latter set to lose economic, political and diplomatic influence. Leaving the 28-country bloc behind could mean Britain would have to replace the existing EU trade deals, a process which could be tortuous and fruitless.

"On trade, the EU has negotiated broadly effective deals for Europe and the UK," Mackenzie said. "Restoring these agreements after Brexit would take years, perhaps a decade, of negotiation."

The negotiations would be "a time-consuming distraction to maintain market access we have today on terms that are likely to be worse", Mackenzie said, adding that "by leaving, the UK would stop being rule makers and become rule takers."

Without Britain, the EU would lose its second-biggest economy and one of the two main military powers. The debate over Britain's role in the union has escalated since the referendum was announced for 23 June.

Supporters of the campaign to leave the EU claim the UK would prosper outside the union and will particularly benefit from the absence of so-called red tape, regulations some see as damaging to Britain's economy. However, pro-European campaigners, who include Prime Minister David Cameron and Chancellor George Osborne, believe the economy would be badly hit.

And the damage would not stop there, according to Mackenzie. "Brexit would inflict a blow on the EU that it can hardly afford given the eurozone and migration crises. Without the UK, the EU would be weaker. British business cannot afford a knock and global leaders are amazed that the UK would even consider leaving," he said.

A number of high-profile political figures from outside the UK, including US president Barack Obama and Chinese president Xi Jinping, have stressed the importance of Britain remaining in the EU, but public opinion remains split.

"The in and out campaigns are really about unilateralism versus internationalism. Most businesses support the EU and internationalism," Mackenzie added. "For Britain to wield the economic political and diplomatic capital it has historically enjoyed, we must vote to remain."