CBI says staying in EU 'overwhelmingly' best for business
Staying in the European Union is worth between 4-5% of UK annual output and "overwhelmingly" best for business - but reforms are needed, the CBI says.
Ahead of its national conference, the business group said research found EU membership is worth £62-78bn to the UK.
It calls for barriers to e-commerce to be removed by the EU, for it to become more outward-looking and for a "re-focus" in the work of EU commissioners.
It also wants to see a permanent opt-out from the Working Time Directive.
The CBI report, compiled after questioning its members, also said business wanted a moratorium on legislation which could be made at national level.
The CBI's director general, John Cridland, said: "We have looked beyond the political rhetoric to examine the pros and cons of EU membership and British business is unequivocal - the Single Market is fundamental to our future.
"We are better off in a reformed EU than outside with no influence. Each year, membership is worth £3,000 to every household in this country."
The government wants to negotiate a new deal with the EU.
Mr Cameron has said the EU needs to change to allow Britain, or other member states, not to be bound by all its decisions.
If he can secure a new deal, Prime Minister David Cameron has pledged a referendum on the UK's relationship with the EU by 2017 should the Conservative Party win an outright majority.
The Liberal Democrat chief secretary to the Treasury, Danny Alexander, said: "This compelling report makes a powerful business case for the UK's continued membership of the EU."
He said he had been told on a visit to India last week that EU membership was one of the reasons why the UK was an attractive place to invest.
The comments come after the group suggested the UK economy was recovering at a "slow and steady" pace.
"The UK is now set fair for growth with confidence returning to Britain's entrepreneurs," Mr Cridland added.
"The recovery won't be spectacular, just slow and steady, but appears more solid and better-rooted."
Shadow minister for Europe Gareth Thomas said: "The CBI's report clearly shows that the business community doesn't want to see Britain sleepwalk out of the EU.
"Today's report shows that Europe brings each UK household £3,000 a year. David Cameron is willing to put this at risk because his approach to Europe is based on narrow party interest, not Britain's national interest."
"Labour believes that a commitment to staying at the heart of the EU, along with a clear programme of deliverable reforms is the best course for Britain.
"Labour has long called for reforms to make Europe work better, including a new EU Commissioner for Growth to help focus Europe on delivering the jobs and prosperity that our country needs."