* Poll: 77 percent of British businesses back EU referendum
* Just over 50 percent thought withdrawal would be bad for business
* Cameron wants to renegotiate Britain's EU ties before vote
Prime Minister David Cameron's flagship policy of reforming Britain's relationship with the European Union before holding an in/out referendum has the support of the majority of British firms, a poll suggested on Wednesday.
The quarterly survey of nearly 4,000 firms for the British Chambers of Commerce (BCC), a business lobby group, found 77 percent were in favour of giving voters their first referendum on EU membership since a plebiscite in 1975.
The BCC poll found just over half of the firms thought withdrawal would be bad for business, compared to a fifth who thought it would be positive.
Cameron's promise in January of reaching a new settlement with Brussels before an in/out vote by the end of 2017 alarmed some of Britain's biggest allies and fuelled talk of London ending its 40-year membership of the bloc.
The economic impact of pulling out has divided business leaders, politicians and commentators and strained Cameron's relations with his Conservative Party's pro-EU coalition partners, the Liberal Democrats.
Cameron hopes his referendum pledge - currently opposed by the Liberal Democrats and the opposition Labour Party - will give him the edge at the next election in 2015.
Six out of 10 of those surveyed thought Cameron's preferred option - staying inside the bloc on new terms - would be good for business, while 11 percent thought it would be bad and the rest were uncertain.
The BCC surveyed 3,906 businesses in May and June.