Briton behind Berlin's building of the decade

Yet that it is what has happened, as this week London-based David Chipperfield, 55, hands over the completed building to a rapturous local reception. "It is the most beautiful work of reconstruction I have seen," one architectural expert told me, "and we have a lot of experience of that in Germany." What he is giving back is no mere repair job, but a building that can claim to be the museum of the decade. Like Frank Gehry's Bilbao Guggenheim in the Nineties, it sets a direction and a standard for others to follow.

But, where Gehry's titanium masterpiece dazzled and awed, the Neues Museum's virtues are subtle, its beauty coming from thousands of individual decisions about details and materials. It is a work of extraordinary patience, the result of years of diplomatic handling of all the intrigue and colliding egos that go with one of Berlin's highest-profile projects. Chipperfield notes that at sensitive moments "black limousines started turning up at meetings", disgorging politicians keen to stick their oar in.

The Neues Museum, which first opened in 1855, was one of the most important of Berlin's exceptional museums, showing a range of antiquities comparable to those in the British Museum. Its star exhibit, which will return when the museum opens to the public in the autumn, is the famous bust of Egyptian Queen Nefertiti.

The museum was bombed in 1943 and 1945, but following the war the East German government was slow to salvage it. Its collections were dispersed, and surviving parts of the building were used for storage. Rain and weather compounded the damage caused by bombs and fire, leaving the neo-classical building, once richly decorated with frescoes and marble, a romantic wreck.

Restoration work finally started in the late Eighties, only for the fall of the Berlin Wall to put it on hold again. Germany's reunified government ran a competition to choose an architect for the museum in 1994, which was won by Italian Giorgio Grassi. Grassi fell foul of the museum's then director, who had wanted Gehry to win the competition, and a second competition in 1997 led to a run-off between Gehry and Chipperfield. The director still wanted the famous American, but the relatively unknown Londoner won the showdown.

His big idea for the project was "soft restoration", which meant keeping the fragments of the original building as he found them, and doing what was necessary to stop further deterioration and make the building work again as a museum.

At times the new work is almost invisible, such as repairing details or replacing lost ceilings unobtrusively. At others it is bold, for example the grand staircase, which is pristine and white amid the gnawed and blackened columns of the old building.

Chipperfield's approach risks making a theme park of destruction, a Disneyland of decay. Such criticism as there has been in Germany has made this point, calling him "an architect of damage". Chipperfield says his work is not about "demonstrating damage" but "demonstrating the beauty that was there in the ruin."

The ¤200million project was ¤30million under budget, but the real achievement is in making a huge building that is endlessly delightful and, as Chipperfield puts it, "moving". He has done this by bringing out, with infinite care, the best of what he found. The Neues Museum is a work of time rather than instant gratification: both the historical time recorded in its walls and its exhibits, and the time put into its renewal by the architect and his collaborators.

Chipperfield first made his name in the Eighties with a shop for Issey Miyake in Sloane Street, and a house for photographer Nick Knight in Richmond, but he is now more successful abroad than here. The Neues Museum might finally get him noticed in his home city.