Angela Merkel has urged the UK not to leave the European Union and delivered a message to British eurosceptics that she was not in London to offer "fundamental reform" of the EU.
"We need a strong UK with a strong voice inside the EU. If we have that we will be able to make the necessary changes for the benefit of all," she said.
In a rare speech to both Houses of Parliament in the royal gallery of the Palace of Westminster, the German chancellor said the unification of Europe following the Second World War brought "almost half a century of peace, freedom and prosperity".
There had been high expectation that Merkel could use the speech to tell David Cameron and the Conservatives that she would be willing to grant some British demands for a renegotiation of its terms of membership. However, speaking in clear English, the German chancellor dashed those hopes.
"Some expect my speech to pave the way for fundamental reform of the European architecture which will satisfy all kinds of alleged or actual British wishes, I am afraid they are in for a disappointment," she said.
Merkel's visit to London - also taking in talks with Cameron over lunch in 10 Downing Street and tea with the Queen at Buckingham Palace - comes at a time when the prime minister is coming under pressure to spell out what powers he hopes to repatriate from Brussels ahead of the in/out referendum on EU membership he has promised for 2017.
Labour's shadow foreign secretary Douglas Alexander seized on the speech as evidence that the prime minister's strategy was not yet working. "Sense that chancellor Merkel’s speech today offered much less to David Cameron than he had hoped or expected," he said.
Merkel did offer some opaque signals that Germany would be willing to reform the EU, but did not make any concrete pledges.
She told MPs and peers that she was also not in London to "deliver the clear and simple message that the rest of Europe is not prepared to pay almost any price to keep Britain in the European Union".
Speaking of her happiness as a former citizen of East Germany at the fall of the Berlin Wall, she said: "I am a personal witness to the possibility that change, and change for the better, is possible. This awareness ought to guide us in this anniversary year. Every generation of politicians has its responsibility - we too, the politicians of today.
"We need courage to bring about a change for the better today just as much as it was needed decades ago. We need to continue to write the success story of European unification for today.
"The challenge we face is nothing less than the question whether Europe will be able to assert its values, its interests and its economic strength that brings prosperity to its people durable also in the 21st century.
"We must renew Europe in keeping with the times so that it may fulfil its promise of peace, freedom and prosperity also for future generations."
Following her speech, eurosceptic Tory MP Mark Pritchard tweeted: "Merkel speech summary: The "Submit" Speech for the greater European good. At least she has been honest about what Germany really believes!"
And Rob Wilson, an aide to George Osborne, rated the speech as "solid" but noted it had "nothing dramatic or new". The Conservative MP added: "Clearly wants EU reform but vague about what and how far."
The red carpet treatment of Merkel is in stark contrast to French president Francois Hollande's recent visit. Last month's Anglo-French summit was held on an RAF base, with the two leaders giving a short press conference in a hangar before visiting a nearby pub for lunch.