Almost 80 per cent of firms believe Britain should stay in the European Union, according to a new survey commissioned by the CBI released today.

A total of eight out of 10 businesses said they would favour remaining in the trading bloc if a referendum were held tomorrow, a survey by the lobby group found. Only 10 per cent thought it was in the UK's interests to leave.

Around 75 per cent of respondents said leaving the EU would have a negative impact on the level of foreign direct investment in the UK, with 35 per cent warning that an exit would reduce their own investment spending. In addition, 86 per cent of firms said an exit would impede their access to EU markets.

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The survey – conducted by YouGov – covered more than 400 businesses which together employ 1.5 million people. Small and medium-sized enterprises (SMEs) were just as likely to favour Britain's continued EU membership.

“This sends a clear message that most CBI members, big and small support UK membership of the EU,” said John Cridland, director general of the CBI. “Firms want what is best for jobs and growth, and there is genuine concern that an exit would hit business investment and access to the world's largest trading bloc.”

However, the survey also found that 42 per cent of respondents thought EU employment law, particularly on working hours, had a negative impact on their business.

The surveyed firms mostly agreed that the UK does have influence within the European Union over the laws and regulations that affect them, with 72 per cent feeling Britain had a voice in Brussels. Also, 65 per cent felt this influence would decline if Britain left the trading bloc.

In a speech in January, David Cameron pledged to hold a referendum on Britain's membership of the EU in the next Parliament if the Conservatives win the 2015 general election.

The Prime Minister vowed to take back powers to Britain from Brussels over the coming Parliament, but many are sceptical of whether he will win the agreement of Britain's fellow EU member states for this.

The survey of CBI members was carried out between 13 June and 20 July, and 415 firms were questioned, including 158 SMEs.