It is being billed as a showdown between Russia's two great opera and ballet companies. Moscow's Bolshoi and St. Petersburg's Mariinsky go head to head in London this month in a cultural clash that has critics licking their lips. Having the two internationally renowned organisations facing off in the same city outside Russia is a rare event, and neither wants to be labelled the loser in London. Critics welcome the opportunity to compare the two powerhouses of classical music and dance. "The Bolshoi and the Mariinsky bring their ancient rivalry to London. That's good news for us," Hugh Canning said in the Sunday Times. But speaking to Reuters, Canning admitted that the two Russian companies could have a hard time filling the seats. "I think it is unprecedented that both the Bolshoi and the Kirov should appear in London at the same time. I mean, it's obviously not entirely satisfactory from the point of view of the box office, this is a difficult time of year at the best of times, especially in very hot weather to get people into theatres," said Canning. The organisers share these concerns, aware that there may not be the demand for tickets to sell out both tours. Lilian Hochhauser, the promoter who is funding the Bolshoi's visit, said there was no need for the two rivals to be spurring each other for better results. "It is said that competition is healthy. But I think both of these companies are on such a high level that they don't need to have to worry about competing and keeping up with the Jones's or Joneskys or what ever, because they have their own level, they would keep to it anyway. They don't need a spur. Although, having said that, naturally, there is always a feeling of 'who is better?'" she said. The Mariinsky's 'The Nose', which marked the centenary of the composer's birth, kicked off 10 scheduled performances of Shostakovich operas and ballets at the English National Opera on Thursday (July 20). That overlaps with the Bolshoi's season at the Royal Opera House, located just a few hundred metres away, which kicked off with Sergei Prokofiev's 'The Fiery Angel' on Tuesday (July 25). In its first visit to Covent Garden, the opera company also performs Modest Mussorgsky's "Boris Godunov" and the ballet troupe takes on works including Shostakovich's "The Bright Stream", banned by Josef Stalin, from July 31. Hochhauser originally intended to take the Mariinsky to London, but fell out with its charismatic conductor Valery Gergiev when he insisted on performing Shostakovich only. She went with the Bolshoi instead. Gergiev has questioned the Bolshoi's repertory in London, which includes the tried and tested "Swan Lake". "How many times can you do Swan Lake in London?" he asked in a newspaper interview. Speaking to Reuters ahead of the opening salvo by the Mariinsky, formerly the Kirov, which performed 'The Nose' late on Thursday, the artistic director said his job was to push boundaries, not just repeat favourites. "Sometimes you have to make unusual decisions and we are not, in principal we are not doing what we do because we have to make money. We are called artists, we have to turn our attention first of all to art, which we serve, which we love. And yes, I love 'Swan Lake' myself and we do it, maybe, still better than most of our colleagues, you know, but we did it many times, if you again come and do it and then again next year come do it and then again, people should suspect that these are a group of artists, good artists, but maybe they just have to fill their calendar and do it again and again and simply they will look for something else," he said. However, Gergiev played down the rivalry between the two companies, saying it was about something much bigger than just him and the Hochhausers. "I'm quite busy with something else, not just the Hochhausers and Bolshoi, (they) maybe take one percent of my time, at best. But thinking of Bolshoi, I'm thinking of Russian culture. To respect Bolshoi is also to respect Mariinsky. You cannot hate one and love the other, there is something sick in this theory," he said. But if Gergiev took home the points on artistic values, Hochhauser and the Bolshoi seem to be on the higher ground when it comes to commercial viability. Hochhauser explained that the Bolshoi ballet was performing four premieres during its four week residence at Covent Garden, and said some tickets were already sold out. "I'll give you one guess about which one is sold out," said Hochhauser. "'Swan Lake'. The public can never have enough of 'Swan Lake', it adores 'Swan Lake'. And what ever you bring here, they are very disappointed if 'Swan Lake' is not included," she added.