Both pro and anti-EU groups agree any referendum would be close.
The Conservatives have not disclosed all the areas they want to reform, but the general thrust of their demand is that they want Britain and other member states to repatriate powers in policy areas such as immigration and social security.
European Commission Vice-President for Economic and Monetary Affairs Olli Rehn told reporters in Beijing, where he met senior Chinese leaders on yesterday, that he was ready to work with Osborne on EU reform.
“It is very important that the UK is an active partner of the European Union. It is better to focus on reform than repatriation [of powers],” he said.