For a director who commands such respect, it is surprising what a rough ride Martin Scorsese has had in recent years. But even with "Mean Streets," "Taxi Driver" and "Raging Bull" to his credit, the going has not been easy. Nor have his peers offered him formal recognition. Despite the superhuman efforts he has poured into his most intimately conceived films -" Gangs of New York" took him 23 years to wrestle on to the screen - he has not won the Oscar for best director. The common thread in these disparate troubles is the dilemma of the movie director: how to combine commercial success with artistic integrity. Several of his 1970s films were both hugely popular and lauded for their art. More recently, he's ticked one or other box, seldom both. Ed Pilkington reports.