Britain would risk losing influence in trade negotiations if it leaves the European Union, the head of the World Trade Organisation (WTO) has warned.
WTO director-general Roberto Azevedo told the European Parliament's International Trade Committee that "the more that a country or a member is in a position to join with others in defending a particular idea or defending a particular agenda, the easier it is to push through its interests."
Catherine Bearder, Liberal Democrat trade spokeswoman in the European Parliament, seized upon Azevedo's remarks.
"UKIP and many Tories claim we can just pull out of Europe and trade using WTO rules, but now even the head of the WTO has turned round and said we are better off staying in."
"Being part of the world's largest trading bloc allows us to get a better deal for Britain and to open up new markets for our businesses overseas."
Matthew Elliott, chief executive of Business for Britain, the Eurosceptic business group, said: "At present the European Commission speaks for all EU member states at WTO meetings, yet many business people in Britain do not feel the European Commission has their best interests at heart.
"Business leaders in Britain are increasingly looking to places like China and India for trade, yet the EU is dragging its feet on free trade deals with these countries. As the World's sixth largest economy, we hope the Government's renegotiation includes getting Britain a stronger voice on bodies like the WTO."
The WTO chief’s comments come after business giants such as Unilever and Airbus, along with City of London bankers, called on Britain to stay in the European Union.
Paul Polman, chief executive of the international consumer goods giant, warned that Unilever could pull back its investments in Britain "kicked against the table" and left the political bloc.
"We will always look at things," he responded when asked if Unilever, which employs 7,000 people in the UK, could reduce its presence in the country.
Meanwhile banks in the City of London said there was an "overwhelming case" for the government to deepen its ties with the European Union.