German Chancellor Angela Merkel has said she is opposed to plans by British Prime Minister David Cameron to increase control over the number of EU migrants entering the UK.

"Germany will not tamper with the fundamental principles of free movement in the EU," Merkel told the Sunday Times.

The German Chancellor’s stance could make it much more difficult for Cameron, who is seeking to address UK voter concerns about immigration, to renegotiate changes to the EU treaty that would allow the UK greater control over its borders – a goal on which he has staked his political future.

Current EU legislation requires each member state to allow workers from any other country of the bloc to live or work there. Cameron has promised to push through changes to the way the EU works and then call a referendum on the UK’s membership in 2017 in 2017 if the Conservatives win the general election in May next year.

While London and Berlin agree on the need to curb so-called benefit tourism by limiting abuse of access to welfare benefits across the EU, Merkel is not open to negotiating the right of people to travel in member states without restriction.

Cameron is believed to be preparing a manifesto pledge to bring in quotas for low-skilled migrants from the EU - a move that could potentially slow the growth of the eurosceptic United Kingdom Independence Party (UKIP), which is seeking to drastically cut immigration to Britain and campaigns for Britain’s exit from the EU. Before the last general election Cameron promised to bring net annual immigration down to the tens of thousands but has failed to get anywhere near the target.

The outgoing European Commission President, Jose Manuel Barroso, last week warned Cameron that he was in danger of alienating Britain’s ‘natural allies’ in eastern Europe with his talk about immigration.

German Finance Minister Wolfgang Schauble on Monday echoed Merkel’s comments, saying that freedom of movement in the EU could not be restricted because it is one of the cornerstones of European integration. 

"That would be incompatible with the European treaties,” Schauble told The Times.“The basic rules of the EU are not up for negotiation.”