The new head of the biggest group of conservatives in the European Parliament dismissed on Saturday demands by British Prime Minister David Cameron to put the brakes on European integration.
Manfred Weber, the new chairman of the European People's Party (EPP), also told a German paper that the group still backed its candidate Jean-Claude Juncker to be the next Commission president despite opposition from Britain.
"The EU is based on an ever closer union of European peoples. That is set out in the treaties. It is not negotiable for us," Weber told the Frankfurter Allgemeine Sonntagszeitung.
"We cannot sell the soul of Europe," he added, also rejecting any demands to let national parliaments win rights to stop European laws.
"If we grant every national parliament a veto right, Europe would come to a standstill," he said.
Cameron, under pressure from anti-EU hardliners in his own Conservative party and in the UK Independence Party (UKIP), has agreed to hold a referendum in 2017 on whether his country stays in the EU. His party is not in the EPP.
Before the referendum he is trying to renegotiate the terms of Britain's membership. He has said that he wants to prevent mass migration and EU interference in police and judicial matters and that he wants national parliaments to be able to work together to block unwanted European European legislation.
Weber said the EPP still fully supported former Luxembourg Prime Minister Juncker's bid to become the next European Commission president.
"We must keep the commitments that we made to our voters: he will be the next president of the Commission," said Weber.
Britain has opposed Juncker's bid, which is supported by several EU members including Germany. Cameron fears Juncker is too aligned to old-school federalists to bring in change.
Citing no sources, Der Spiegel magazine reported that conservative Chancellor Angela Merkel did not want Social Democrat (SPD) Martin Schulz to become Germany's Commissioner in Brussels despite pressure from SPD leader Sigmar Gabriel.
Merkel leads a 'grand coalition' with Gabriel's SPD.