Choreography is a mystery art. How it happens - or indeed what happens - is as elusive to define as pinning down a brainstorm. There is no solid stuff, no rules, no pre-formed maxims, everything moves; the choreographer goes into a studio, finds some dancers, finds some music, finds some moves, finds some light and atmosphere - and this agglomeration of variables goes out on stage all too often to fall flat, a soufflé that didn't rise. It was insufficiently skilled, or its ingredients were stale, or it lacked the leavening of a compelling imagination or the flavour of real emotional imperative. But what is going on?

It would be tough for any Russian ballet company to come into worldly, balletwise London just ahead of the great Bolshoi, but the Mikhailovsky Ballet make a very pleasing impression in their first week at the Coliseum with a pretty and historically interesting Swan Lake and a gently antique Giselle, and dancing that more than most underscores the rare pleasures of period style.

You need very little for a Swan Lake. Tchaikovsky’s music, white swan-girls, a mooning boy, and 32 fouettés for the ballerina in black. That's about it, isn't it? Every traditional Swan Lake we see now is a sort of balletic pizza - a musical base scattered with ingredients collected from a familiar buffet, piled up by its stager or so-called choreographer according to taste (and often a large measure of vanity for sauce).

The Bolshoi Ballet and its London promoters have confirmed wholesale casting changes to the Covent Garden tour starting next Monday, due to the last-minute absence of prima ballerina Svetlana Zakharova. Zakharova was due to give six performances, but has withdrawn due to a hip injury, it is said. Her partner the celebrated male star Nikolai Tsiskaridze has withdrawn from Giselle, and appearances by another senior ballerina Maria Alexandrova have also been reduced.

The Bolshoi Ballet and its London promoters have confirmed wholesale casting changes to the Covent Garden tour starting next Monday, due to the last-minute absence of prima ballerina Svetlana Zakharova. Zakharova was due to give six performances, but has withdrawn due to a hip injury, it is said. Her partner the celebrated male star Nikolai Tsiskaridze has withdrawn from Giselle, and appearances by another senior ballerina Maria Alexandrova have also been reduced.

The annual tradition that is the Royal Ballet School Matinee at Covent Garden isn’t just some prestige indulgence for the nervous parents of ballet children fortunate enough to survive the militaristic training and dogged enough to want to continue into the beckoning career where there are such frail job prospects. It is a place where the gap between a good student and a potential artist comes clear through the sheer size and one-offness of the occasion.

The gallery has been turned into a little girl’s dressing-up closet. The walls are painted midnight blue and dusted with glitter. Ballet shoes, made for small feet, and a discarded tutu are to be found in a decorous pile on the floor. There are shiny trinkets and princessy things and pictures of ballerinas in bright, pastel shades. And miniature cabinets, almost empty but for one or two small objects – old, discardable things that might be hoarded away as treasures by a child wrapped up in its own imaginary world.

Hans van Manen does basic instincts in ballet better than anyone alive. The Dutch choreographer, nearly 78 and far too little exposed in Britain, is a near-contemporary of Kenneth MacMillan, another specialist in sexual relations, but where MacMillan is fascinatingly drenched in guilt, Van Manen takes a bold, guilt-free stand. Grosse Fuge, which Birmingham Royal Ballet revived in the Hippodrome last night in a smart triple bill to entertain all tastes, is all about mating display - four men in black oriental skirts and big-buckled belts, four women in beige Playtex-type corsets that give them mumsy boobs and look unusually sexy.

Within two bars of the overture starting, the first flashes could be seen. English National Ballet’s arena Swan Lake at the Albert Hall - they make no bones about it now - is intended for people who rarely go to the ballet. Actually it is in many cases for people who have no compunction about talking and taking pictures through the ballet quite routinely.

A second coming for Michael Clark's recent Barbican commission Come, Been, Gone. Eight months after the London premiere (on which I opined unenthusiastically below last October), he has added another 20 minutes of choreography, they said, with new costumes and artworks. The revision is also now artfully retitled Come, Been and Gone. Not comma-Gone. And Gone. Makes all the difference.