The Olympic flame makes a dramatic arrival in London on Friday to tour the capital before it plays a starring role in the opening ceremony in one week's time.

A Royal Marine commando will abseil from a helicopter with the torch, which will spend the night safely housed in the Tower of London, where the Queen Elizabeth II keeps her ceremonial jewels.

The 8,000-mile (12,800-kilometre) relay culminates in the capital after snaking around Britain and visiting the Republic of Ireland.

Its arrival will add to the anticipation building ahead of the Games.

Snatched press photographs show that preparations for the opening ceremony next Friday are at an advanced stage, with the show orchestrated by Slumdog Millionaire director Danny Boyle featuring an idyllic English village.

Much of the £27 million ($42 million, 34 million euro) ceremony remains under wraps.

As the preparations for the Games intensify, the competitors are limbering up.

The US basketball 'Dream Team' spearheaded by superstars Kobe Bryant and LeBron James underlined their status as gold-plated favourites as they ran out easy winners against the Great Britain team, winning a warm-up game 118-78 in Manchester.

The Dream Team's form contrasted with the bad news for tennis star Rafael Nadal, who has been forced to pull out of the Games because he is not in the shape to compete after struggling with tendinitis in his knees.

The man expected to be the star of the London Games, the world's fastest man Usain Bolt, is also struggling with fitness.

The reigning Olympic 100 metres and 200 metres champion has been given a new orthopaedic bed at the Jamaica team's training base in Birmingham, central England, to ensure a longstanding back problem does not flare up.

Bolt will not compete at a top meeting in Monaco on Friday after complaining of tightness in his hamstring in the aftermath of his defeat by compatriot Yohan Blake at the Jamaican Olympic trials last month.

Preparations for the Games have been dogged by concerns over security after a firm supplying private guards for venues said it could not supply all of the 10,000 it had promised.

But London 2012 chief Sebastian Coe insisted security would not be compromised, as the government had drafted in 3,500 extra troops to cover the shortfall by security giant G4S, with another 2,000 on standby.

"This is not an issue that has remotely compromised security. This was actually about the supply and the mix, it's never been about the numbers," Coe said.

Coe however got into a testy exchange with an interviewer about criticisms of the organisers' approach to protecting sponsors' rights.

Asked by a BBC radio presenter if he would be able to wear a Pepsi T-shirt to the Olympics, Coe replied "No, you probably wouldn't be walking in with a Pepsi T-shirt because Coca-Cola are our sponsors and they have put millions of pounds into this project but also millions of pounds into grassroots sport."

"It is important to protect those sponsors."

Asked whether he could wear Nike trainers, since Adidas are a sponsor, Coe added: "Let's put some reality in this. You probably would be able to walk through with Nike trainers. Does that satisfy you?"

During a tour of security at the Olympic Park in east London, interior minister Theresa May also said security had not been compromised.

"What I've seen here is a very organised control room, people absolutely focused on their role of providing the safety and security for the Olympic Games," she said.