Nittve: "A little bit homesick"

"After some hard thinking and a tough decision I decided to go," Mr Nittve said, citing homesickness as one of his reasons.

The Stockholm-born 47-year-old is to return to direct the Moderna Museet where he was senior curator from 1986 to 1989.

Tate Trustees will now begin the search for a successor both in Britain and abroad.

The successful candidate, to take over in November, will need to work closely with Sir Nicholas Serota who is the overall director of the Tate.

Sir Nicholas is generally considered the mastermind behind the Tate Modern phenomenon.

Adrian Searle, The Guardian's art critic told BBC News Online that he would "hate to speculate" as to the successor, but added that it matters "a great deal" who they choose.

Mr Searle said that now that the Tate has achieved a high public profile it could turn more attention to its exhibitions.

Though Tate Modern's permanent collection has been popular, its exhibitions, with the exception of the massive sculptures by Juan Mu�oz and Louise Bourgeoise, have not been.

"Tate Modern was supposed to be an art gallery, but they've got a tourist attraction," said Mr Searle.

Tat Modern has been an unreserved success

"What Tate Modern needs is somebody who has a high international profile, who can lead a team and really understands contemporary art."

He admitted that there are very few people in Britain who fit that bill, and thinks that the search will almost certainly be international.

Time Out's art critic Sarah Kent agreed that foreign candidates will be considered, though she is less sure that the job is all that desirable.

Mastermind

"Nittve was a very charming and highly qualified man," she said.

"But I can't envisage what his role was, and I don't think that he had much independence."

The gallery employs high profile curators who take care of the hanging and choosing of work.

Tate Modern holds classic international works from the past century including pieces by Warhol, Lichtenstein and Pollock.

One of the keys to its success with the public has been its exhibiting of art works by themes.

The gallery is in a former power station

To the onlooker the Tate Modern director's role seems to be to excite interest in the gallery and conduct relations with the public and the media.

There is speculation that Julia Peyton Jones, who revived the fortunes of the Serpentine Gallery in London, could be a possible candidate.

But it is equally possible that a highly qualified, less well-known candidate could present themselves from abroad.

And it is a possibility, if remote, that Mr Nittve would not be replaced and Sir Nicholas would take control of Tate Modern as well as general directorship of the Tate.