Royal Ballet: Swan Lake, Royal Opera House, London

Dancers grow into roles. Unlike actors, they rarely get the chance to polish their interpretations in previews. That happens with later performances. In the Royal Ballet's current run of Swan Lake, Zenaida Yanowsky and Alina Cojocaru are changed Swan Queens. Yanowksy has a new partner, and new confidence. Cojocaru has rethought her whole approach to the role.

Yanowsky is the Royal Ballet's tallest ballerina, and finding her a partner has always been tricky. The Danish-trained Kenneth Greve is 6'4", with a dramatic approach that suits Yanowsky's. The real news of this performance, though, was his ballerina's increased maturity. Over the past year, Yanowsky has grown visibly stronger, and it shows in her Swan Lake. She has opened up her torso: there's a new dignity to the carriage of her head, and much greater force to her dancing. Her back and wrists can still be unyielding, but the whole performance has gained authority.

Yanowsky has always been an intelligent actress, and she makes expressive use of her improved technique. Odette, the enchanted Swan Queen, keeps moving away from her prince and returning to him, caught between fear and the need for reassurance. Yanowsky gives her arabesques a look of yearning flight. As she turns away, she slows down, already regretting it.

As Odette's wicked double, she keeps changing the pace of her dancing - darting forwards, melting back. She takes gleeful risks in seducing the prince, sailing triumphantly off-balance in the sure knowledge that he'll catch her. Her most touching moment comes in the last act. Finding that her prince has betrayed her, she explains in mime that she must die. The gestures are grand, but softly phrased: she doesn't reproach him, she despairs.

Alina Cojocaru's London debut in Swan Lake was a disappointment. She has an effortless flow of movement, and she used it to fill her dancing with curlicues: all icing, not enough cake. Two years on, she's much better.

If Yanowsky is the Royal Ballet's tallest Odette, Cojocaru is its tiniest. Her lightness and speed suit the choreography. That current of movement is still there, and her dancing has absorbing detail. Even so, Cojocaru isn't quite a Swan Queen. She needs more grandeur. Her performance is full of good things, but it isn't yet a complete account of the role. Yanowsky and Cojocaru have more performances to come: both have the chance to develop further.

This is a lively revival of Anthony Dowell's production, with good supporting performances. Genesia Rosato brings a vivid sense of family dynamics to the prince's mother - you feel this isn't the first time his mum has asked why he isn't married yet. In the Neapolitan variation, José Martin dances with a lovely touch of raffishness.

In rep to 25 January

(020-7304 4000)