Swan Lake, Mariinsky Ballet, Royal Opera House

For a dance company, the always delicate balance between preserving your heritage and creating an exciting future becomes especially hard to negotiate when you are the most venerable institution in your field. The Mariinsky Ballet, now on tour in London, have this problem magnified by a general perception (theirs and the public’s) that they are the world’s keepers of the great Russian ballet tradition, which they are expected to represent at its finest.

Their 1950 Sergeyev staging is almost as dated as the Lavrovsky Romeo and Juliet they showed earlier in the week, and has, somewhat surprisingly, a very similar Italian quattrocento setting (with extra pointy medieval headdresses for the women in the court scenes). It’s pretty enough, but as dated as – and coloured in much the same tones as – an aquatint photograph, and yesterday’s matinée performance showed it teetering dangerously close to museum-piece territory, despite the presence of much-hyped young British dancer Xander Parish.

There’s a glitter to Parish’s story: talent-spotted in the corps of the Royal Ballet and lured to Russia’s oldest ballet company by its director, Yuri Fateyev, who promised Parish the star roles the Royal Ballet had precisely no interest in giving him. But this fairy tale has a context: Fateyev has been stocking the top ranks of the Mariinsky with dancers from "outside", and while it has obviously been to Parish’s benefit, there are plenty who see Fateyev’s policy as disastrous for the company.

Parish acquitted himself manfully as Siegfried. He looks just right - ever so handsome with the tall, sculpted physique directors love - but it is a tricky part to act. Siegfried’s choreography presents him as a stuffed shirt dullard, and faithless lover to boot; you need to emote all over the shop to get the audience to like him, but poor Parish looked like he was trapped in a suffocating Russian heritage Siegfried suit, which kept his back and shoulders constantly scraped back in maximally “grand and aloof” setting and never allowed him to run messily or collapse in grief.

He never looked particularly in love either, but the famous lakeside pas de deux is fiendish, and both he and Odette/Odile Yulia Stepanova were concentrating too hard on the steps throughout to be able to do much about their lack of immediate chemistry. Stepanova’s acting was better overall, mustering both Odette’s fragility and Odile’s minxiness, but then the part helps: all the emotions of the elegant and affecting swan-woman are there in Ivanov and Petipa’s steps, which still remain a choreographic masterpiece for their combination of form and emotion. Stepanova is Vaganova trained and does beautiful swan arms, but I still couldn’t shake the feeling that she too was trapped into performing the part faithfully, rather than living it.

These two are still quite junior for principal roles (Parish is a Second Soloist, Stepanova one step lower, a coryphée): I wouldn’t necessarily expect them to be perfect, but it’s sad to see them so nervous (such a contrast to the equally-young dancers debuting in ENB’s Coppélia last week). If the Mariinsky’s directors think Parish and Stepanova have potential, they should be encouraging them to relax and feel and grow in the part, not constricting them with weighty tradition.

I hold Boris Gruzin (conducting the Mariinsky Theatre orchestra instead of the advertised Alexei Repnikov) responsible for much of yesterday’s tedium: he took Tchaikovsky’s score at a glacial pace that seemed designed not to raise any heartbeats. The corps de ballet were neat, and some were charming (the pas de trois in Act I, scene 1, the Hungarian dance in Act II), but with that musical deadweight the two court scenes, with their parades of jolly dances, were bound to drag. Soslan Kulaev was the dullest old tutor I’ve ever seen: in a black velvet scholar’s cape and hat he was the spit of a Holbein painting, but considerably less lifelike. The sparky jumping of Grigory Popov as the jester supplied some much-needed fireworks, but not many laughs - it’s hard to laugh at a jester whose creaking smile and heavyset frame suggest he has a moonlight sideline in duffing up the prince’s political opponents.

There is more to like at the lakeside, where the slender women of the Mariinsky’s corps can still make lyrical, tender work of Ivanov’s fabulous choreography. But the best bit is when Andrei Yermakov’s Rothbart explodes onto the serenely moonlit stage like a raven blown in hurly-burly on a hurricane: sinister and explosive in black and silver feathers, his fey, spiky jumps crackle with the energy so lacking elsewhere.

Audiences may love this museum piece – or feel they ought to – because it’s authentic Russian ballet. But Russian ballet also gave the world Diaghilev, Stravinsky, Balanchine, Fokine and Ratmansky, all of whom are featured in the two mixed bills the Mariinsky will present next week.  Those will have a lot of work to do to prove that the company can still do excitement, beacause this ossified Swan Lake is not just living in the past: it’s dying in it.

• The Mariinsky Ballet are performing Swan Lake at the Royal Opera House until 14 August and other productions in repertory until 16 August.