By Kylie MacLellan and Guy Faulconbridge
LONDON (Reuters) - An ally of German Chancellor Angela Merkel said on Monday it would be unrealistic for British Prime Minister David Cameron to expect to achieve changes to European Union treaties before the country holds a referendum on its membership of the bloc.
The comments come days after Cameron, who has said treaty change is needed to reform Britain's EU ties ahead of a vote by the end of 2017, embarked on a tour of European capitals to discuss his plans with key EU leaders.
Following a meeting with Cameron in Berlin on Friday, Merkel promised to work with him to clinch a deal, saying treaty change was not "totally impossible".
Norbert Roettgen, chairman of the foreign affairs committee in the German Bundestag and a lawmaker in Merkel's Christian Democrats, said Germany wanted to keep Britain in the EU but had to look at what was feasible.
"To have treaty change is a huge political venture and you need to invest huge political capital and risk," Roettgen told reporters in London.
"To have a consensus about the content and then to have the procedure of treaty change within two years I would say this is simply not realistic."
PARTY SPLIT
Merkel has previously supported the idea of treaty change to secure closer integration of euro zone countries, but German officials have said there is little appetite now in other European capitals for a major reworking of EU rules.
Cameron, elected for a second term last month, has said the relationship between London and Brussels is not working in Britain's interest and while he wants to stay in a reformed EU, it would not break his heart to leave.
Roettgen said he believed the vote was more about tackling a decades old split within Cameron's Conservatives over the EU than solving the bloc's problems. He said Germany would prefer Britain held the vote as soon as possible.
Cameron has said it could be brought forward if he completes his renegotiation earlier.
The British leader is due to set out his proposals in more detail at a meeting of EU leaders on June 25-26, but has been clear that changes to EU migrants' access to welfare payments in Britain will be key.
Roettgen said EU member states would not accept changes to the bloc's freedom of movement rules.