Chancellor Angela Merkel said ahead of an EU summit that Germany would not give in to Britain's demands for EU reform if it meant sacrificing achievements made by the bloc in forging integration.

"On the one hand, we want to reach an agreement with the British government... on the other hand, we will not put the fundamental achievements of European integration in question, in particular, the principles of freedom of movement and non-discrimination of European citizens," said Merkel in an address to parliament.

"These principles are not up for debate," she said, on the eve of an EU summit when Britain's demands are to be discussed.