LONDON (AFP) - German Chancellor Angela Merkel began a visit to Britain Thursday, where she will make a historic speech to parliament, hold talks on the EU and Ukraine with Prime Minister David Cameron and take tea with the queen.

The eyes of Europe will be on how the continent's most powerful politician deals with Cameron's efforts to win her support for his bid to reform the bloc ahead of a referendum on Britain's membership.

Merkel is expected to speak in German when she addresses lawmakers from the House of Commons and the House of Lords, the first time a chancellor of a reunited Germany has addressed both houses.

She follows in the footsteps of US President Barack Obama and French ex-president Nicolas Sarkozy in speaking to the twin chambers of parliament at Westminster.

The German embassy confirmed she had landed in London in what it called an "important day for Britain and Germany".

Cameron said that during his talks with Merkel at his 10 Downing Street residence they would have "discussions on EU reform and Ukraine", where a bloody political crisis is increasingly putting Russia and the West at loggerheads.

The British premier has rolled out what one newspaper called the "most vermillion of red carpets" in his bid to woo fellow Conservative Merkel over his plans to rewrite the European Union's treaties to repatriate some powers to London.

Despite Merkel's general sympathy towards Cameron's views and the pair's good personal relationship -- reported to have been bolstered during a Cameron family visit to her country home last year -- experts warn that he is unlikely to extract much.

"Merkel is caught between a rock and a hard place. On the one hand she would like to help Cameron out of the corner, as Germany wants Britain in rather than out," said Almut Moeller of the German Council on Foreign Relations thinktank.

"But in effect, her real game is the eurozone and therefore she will not keep Britain in the EU at all costs. And the rest of Europe will listen carefully to what she says in the British parliament."

A recent warming in ties between Germany and France -- the traditional axis of the EU -- also threatens to scupper Cameron's efforts to extract reforms.

According to the Times newspaper, Merkel will rebuff Cameron's calls for limits to freedom of movement for workers within the single market, but echo his concerns over so-called "benefit tourism".

British newspapers have also reported that Merkel favours giving Cameron special deals to help it remain in the EU, although at a level that does not require full treaty change by the bloc's 28 members.

They have suggested these could be made under EU rules similar to those that were used to set up bailout funds during the eurozone financial crisis.

Merkel will also meet opposition Labour party leader Ed Miliband and Liberal Democrat leader Nick Clegg, who is the deputy prime minister in Cameron's coalition government.

She will round off her visit with a trip to meet Queen Elizabeth II at Buckingham Palace.

Cameron hopes to win over voters in Britain's in-out referendum by securing reforms that would dilute Europe's influence over domestic policy, but is finding support from fellow EU nations hard to come by.

Cameron has said the vote will be in late 2017, provided he is re-elected in 2015.

Gunther Krichbaum, chairman of the commission on European affairs at Merkel's Christian Democratic Union (CDU) party, told the Guardian newspaper that renegotiating treaties was "definitely not an option."

During their 90-minute talks over lunch, Merkel and Cameron are also expected to address a proposed EU-US trade deal and the identity of the next European Commission chief following Jose Manuel Barroso's departure in 2015.

Cameron is hoping for a like-minded appointment, but the Times reported Merkel was about to back former Luxembourg prime minister Jean-Claude Juncker, who Britain fears may be too federalist.

Juncker said Thursday he was ready "in principle" to run.

Merkel's speech to members of both chambers of parliament is the first by any German leader since President Richard von Weizsaecker did so in 1986.