David Cameron rejected demands for an “in or out” referendum on Europe today as he vowed to fight to maintain Britain’s influence in a rapidly changing European Union.

The Prime Minister risked further strife with Conservative Eurosceptics by talking up the “real benefit” of EU engagement a day after 100 Tory MPs urged him to promise a referendum on Britain’s relationship with Europe following the 2015 election.

At a press conference in Brussels, Mr Cameron described himself as a “practical Eurosceptic” who completely understood why some people wanted an “in or out” referendum. But it was not “the right thing to do”.

But he was careful to leave the door open to an eventual referendum on the new Europe that emerges as the 17 eurozone nations press ahead with banking, fiscal and political union in the next few years.

The Prime Minister said: “Europe is changing. There is a change taking place as the countries of the eurozone follow the remorseless logic of having a single currency but having 17 different finance ministries and all the rest of it. They need to change and they recognise that.

“That change has consequences for Britain. My job is to make sure we secure all the safeguards that we need so that our role in the European Union, our access to the single market, our say in the single market, is properly safeguarded.”