* 72 pct of Britons doubt Cameron can reform EU - poll
* Data shows voters split on whether to stay in EU
* Majority feel Britain short-changed by EU relationship
Nearly three-quarters of Britons doubt that Prime Minister David Cameron will succeed in a bid to renegotiate the country's relationship with the European Union, polling data released on Sunday showed.
The large-scale poll showed public opinion split on whether Britain should leave the 28-country bloc but highlighted widespread discontent among voters about the ways in which the country benefits from its EU membership.
The data, gathered from 20,000 respondents, will come as a blow for Cameron just a week after he set out seven key policy areas, including judicial powers and immigration, where he hopes to reshape Britain's ties with the EU.
Faced with eurosceptic factions in his Conservative Party and voters defecting to the anti-EU UK Independence Party (UKIP) Cameron has promised to negotiate sweeping reforms to the EU and, if re-elected next year, to hold a referendum by 2017 on whether Britain should stay in it.
The poll, released by former Conservative party deputy chairman Michael Ashcroft, showed 72 percent said they had "little or no confidence", or "not a great deal of confidence" that Cameron could negotiate a better deal for Britain. Just 4 percent expressed a "great deal of confidence".
"Many like David Cameron's plan to negotiate better terms for Britain," Ashcroft said. "The trouble is, three quarters of them doubt it will work."
"Most of the pessimists think other countries will not be prepared to make concessions to Britain however well the PM (Prime Minister) argues the case."
Cameron has so far received a lukewarm reception for his renegotiation bid from European leaders.
French President Francois Hollande poured cold water on the prospect of major EU treaty changes while a high profile visit to Britain by German Chancellor Angela Merkel yielded only limited backing for reforms.
The Ashcroft poll, which was conducted in January this year, showed that 41 percent thought Britain should leave the EU, with an equal proportion supporting continued membership.
Cameron's party is expected to suffer in European elections next month as voters increasingly turn to UKIP to express their frustration with a perceived interference in British affairs by European authorities.
The poll said that 49 percent of people think the costs of EU membership outweigh the benefits, with only 31 percent holding the opposite view. A 62 percent majority believe other countries get more out of EU membership than Britain does.
"Many associate the EU with excessive immigration, unnecessary rules and regulations, and paying for other countries' economic problems," Ashcroft said. "Even pro-Europe voters are exasperated by the waste and inefficiency of Brussels institutions."