The new special relationship: Cameron rolls out the red carpet for chancellor Merkel

Angela Merkel will enjoy a state visit in all but name tomorrow, as David Cameron tries to use his warm relationship with her to secure European objectives.

The German chancellor will be given the rare honour of addressing both houses of parliament and a meeting with the Queen, but Tory eurosceptics will be looking on warily as they assess how likely she is to help Cameron provide some opt-outs from EU regulations.

The trip will be in sharp contrast to the no-nonsense visit offered to French president Francois Hollande recently, who waslimited to an afternoon in the pub with the prime minister.

Cameron desperatly needs German support for British negotiations about its relationship with the EU ahead of a forecasted referendum in 2017, but comments from European officials suggest Merkel's offers will fall far short of the radical demands of Tory backbechers.

Cameron enjoys a measure of goodwill from Merkel, after the two struck up a close personal friendship during previous visits.

One Downing Street source told the Mail on Sunday Merkel views the British prime minister as a "naughty nephew".

Cameron gave the German chancellor a boxset of Midsomer Murders after the pair spent a weekend at Chequers binging on the detective series.

Merkel shares Cameron's conservative instincts and desperately wants Britain to remain in the EU, but she is decidedly more progressive in her branch of centre-right  politics than the Tory leader.

Her pragmatic, unfussy approach to politics has proved a hit with German voters and allowed her to win a third term, with her party securing its best result in 20 years.

Merkel is prepared to give Cameron special assurances in a revised EU treaty, including limited opt-outs and a more flexible approach to EU regulation.

She will reportedly offer the PM 'targeted' treaty changes, new clauses protecitng non-eurozone members from being outvoted on single market issues and a possible NHS opt-out from the working time directive.

But Downing Street is being told to adopt a more hard-headed approach to the prospect of EU negotiations, as it warns that Germany is just one of 27 EU countries which needs to be courted for Cameron to secure a revision to the Lisbon treaty.

"There is perhaps too much optimism emanating from No 10," a Foreign Office source told the Guardian.

"We have to be a very hard-headed about this and bear in mind that the bedrock of the EU is the Franco-German relationship.

"There is only so far the Germans will go. We should be making a much bigger effort with the French."

Labour shadow Europe minister Gareth Thomas said the gap between what Conservative backbenchers are demanding and whatMerkel is offering "remains unbridgeable".

He added: "Europe does need to change, but the tragedy for Britain is that since being elected, David Cameron seems to spend more time negotiating with his backbenchers than with other EU leaders."

Former Liberal Democrat leader Menzies Campbell said: "Anyone who believes that Merkel, who is after all the leader of a coalition, is going to come to London with the kind of agenda that would satisfy the most rabid anti-Europeans in the Conservative party has got another thing coming.

"Germany and France have been the engine room of the EU, often resentful of the fact that Britain appeared from time to time to be disconnected.

"Why should Merkel offer some kind of unique relationship for the UK under a Tory party which embarrassed her by leaving the European People's party [in the European parliament] as soon as the 2010 election was over?"