THE London Olympic Games open tonight with a £27 million extravaganza, amid speculation that Sir Roger Bannister – the first man to run a mile in less than four minutes – will light the cauldron to officially launch the biggest show on Earth.

However, it was revealed last night that tickets for the opening ceremony have not sold out and some people who have paid up to £1000 for seats will only get a restricted view.

Details of the event – choreographed by film director Danny Boyle – remain shrouded in secrecy, despite footage of recent dress rehearsals being leaked on to YouTube. Some clips were pulled from the website yesterday on copyright grounds as organisers stepped up efforts to keep any information about tonight's highly anticipated curtain-raiser under wraps.

A YouTube spokeswoman said: "When we're notified a particular video uploaded to our site infringes another's copyright, we remove the material in accordance with the law."

However, an official video clip, released by the organisers, showed dancing nurses and hospital beds in a celebration of the National Health Service.

It has also emerged the 10,000 performers – a mix of professionals and volunteers from all walks of British life – will be joined by farmyard animals including 70 sheep, 12 horses, 10 chickens, three cows, two goats and even dogs and geese as Boyle transforms the Olympic stadium into a homage to the British countryside.

It is estimated the show will be watched by a worldwide audience of up to four billion.

Possibly even more top secret than the opening ceremony entertainment, however, is the identity of the person chosen unanimously by the London organising committee to be the final torchbearer who lights the Olympic cauldron.

Last night Sir Roger, 83, emerged as favourite as bookmaker William Hill said the odds on him lighting the flame had been slashed to evens. A spokesman said 98% of bets placed yesterday were on Sir Roger.

He added: "A week ago we were 33/1 for Sir Roger; although he was an amazing sportsman we felt that his connection was not Olympic enough."

Sir Roger has already carried the Olympic Flame during its relay around the country, along with second favourite Sir Steve Redgrave, a five-time gold medal winner. However, the rower said earlier this week he thought it unlikely he would be asked.

Ladbrokes and Coral also reported a surge of interest in Sir Roger.

Meanwhile, it has emerged there could still be empty seats in the stadium with tickets in the most expensive areas still not sold out with 24 hours to go. Tickets were still available in section AA, carrying a price tag of £2012 each, and in section A, where they cost £1600. They are available as part of a hospitality package.

There were also fears that spectators who have forked out almost £1000 for last-minute tickets will not get a good view of the whole event. A message on the London 2012 tickets website says that seats bought after July 17 for £995 and £150 will have a restricted view of parts of the ceremony.

London mayor Boris Johnson told a reception the city was ready to host "the greatest Olympics that has ever been held". Speaking to an audience of politicians, royalty and Olympic dignitaries he also sought to reassure US presidential candidate Mitt Romney of the UK's readiness for the Games after criticism by the Republican.

In an NBC interview, Mr Romney, asked if Britain was ready for the Games, replied: "You know, it's hard to know just how well it will turn out.

"There are a few things that were disconcerting, the stories about the private security firm not having enough people, supposed strike of the immigration and customs officials; that obviously is not something which is encouraging."

Mr Johnson said the capital was poised for that "climactic moment when some mysterious superstar will ignite the cauldron and the Geiger counter of Olympo-mania that has been spreading through the city will go off the scale".

In a mock pantomime moment at the reception, Mr Johnson said he wanted to "elucidate" the situation for Mr Romney, asking guests if they thought Britain was "ready", prompting cries of "yes". He added: "The stadium is ready, the velodrome is ready, the aquatic centre is ready, the transport system is running absolutely brilliantly."

He said Home Secretary Theresa May had confirmed security arrangements were under control, and jokingly added: "The weather is ready, thanks to the ministrations of Weather for London who have put in these new cloud lanes to stop the rain."

Mr Johnson said the athletes' village was also ready, boasting it is "more luxurious than Center Parcs, it is swankier than the swankiest Mediterranean or Marbella timeshare, with a much rosier economic future".

Continuing to raise laughs, he said: "I can confidently predict my Lord Mayor, since you worry about these things, that Team GB will win enough bronze and silver and gold doubloons to pay the debt of Greece and Spain."

Before leaving to visit another celebration event, the mayor sparked applause, telling the reception: "I think we can hold the greatest Olympics that has ever been held."