Three million jobs could be at risk if Britain does not stay at the heart of Europe, leading businessmen have suggested.
In a letter to the Daily Telegraph, a group of 20 businessmen urged the Government to seize opportunities to "re-engage in the decision-making process" in the European Union, arguing that Europe's future is vital to Britain's economic interests.
Signatories include Virgin boss Sir Richard Branson, British Telecom chairman Sir Mike Rake, and Sir Martin Sorrell, chief executive of advertising group WPP.
Their intervention comes 10 days after David Cameron vetoed EU treaty reforms.
They write: "The Government estimates that three million British jobs rely on exports to our European partners.
"The EU's institutions, from the commission to the European Court of Justice, exist mainly to safeguard the single market's level playing field. Protecting the single market has to be the bedrock of our re-engagement with Europe."
The wealth creators also argue that it is in Britain's interest for the euro to survive, and that the EU's single market is "of great importance" to the UK, adding: "It accounts for over half our trade, but we must deepen and widen it, and push for reform in services, telecoms, the digital arena and energy."
European countries on Monday agreed to provide 150 billion euro (£125 billion) to the International Monetary Fund (IMF). But Britain's decision not to take part in a scheme to support the struggling eurozone meant EU finance ministers failed to reach their target of 200 billion euro.
Britain has made clear that it will not be part of any effort intended specifically for the eurozone, but is ready to consider participating in a global effort to boost IMF resources at a meeting of the G20 group of major economies in Mexico in January.
Responding to the business letter, UK Independence Party leader Nigel Farage said: "This is pretty desperate stuff and those that have signed the letter should really know better. A distorted picture has been painted to suggest that the UK would not be able to trade with the EU when it ceases to be a member state. This is simply scaremongering as there are many non-EU countries such as China, the US, Switzerland and Norway who happily do business with the EU."