David Cameron should not expect any favours when he tries to renegotiate powers back from Brussels, MPs have warned.
The influential Commons Foreign Affairs Committee said the other 26 European Union states would not be ready to "pay any price" to persuade Britain to remain a member
Cameron is banking on winning powers back from Brussels before a referendum on Britain's membership is held after the next General Election, if the Tories win.
But the MPs said they were "sceptical" of the chances of other member states being willing to renegotiate EU law to allow the UK to reduce the level of its integration.
The cross-party committee welcomed Cameron's promise to seek a new settlement for Europe if he wins the 2015 general election, but warned that he is more likely to succeed if he pushes for reform across the whole EU rather than special treatment for the UK.
The report did not reach a judgment on whether the UK was better off in or out of the EU, but it said that, while closer integration between EU states could make it more difficult for the UK and other non-eurozone countries to shape the rules of the single market, it did not make Britain's continued membership "impossible or worthless".
The committee urged the Government to take a "constructive and co-operative tone and approach" when pushing the case for reform.
It said that given that it is over a year before "any major EU treaty reform process seems likely to get under way", it is impossible to assess whether Mr Cameron could win the kind of settlement he might want.
"However, we are clear that UK proposals for pan-EU reforms are likely to find a more favourable reception than requests for further 'special treatment' for the UK.
"We are sceptical that other member states would renegotiate existing EU law so as to allow the UK alone to reduce its degree of integration, particularly where this could be seen as undermining the integrity of the single market.
"Our sense is that other member states want the UK to remain an EU member.
"However, we do not think that a UK Government could successfully demand 'any price' from other member states for promising to try to keep the UK in the union."
The report found there was "support for some of Mr Cameron's reform ideas around the EU and significant scope for further progress on deepening the single market, pursuing free trade agreements ... and improving the quality of the EU's regulatory practice".
But it warned there was little appetite among other member states for further treaty change.
"Many member states would be reluctant to embark on a major EU treaty amendment process under current rules, because of the amount of time involved and the risk of any new treaty failing at the ratification stage, especially if one or more referendums were to be held," said the committee.
"There appears to be a growing body of opinion that EU treaty change requiring unanimous agreement and/or ratification by all member states may no longer be possible."
Cameron's timetable of completing negotiations in time for a 2017 in/out referendum on EU membership "might be achievable" but the process could drag on beyond this date, the committee warned.