The Olympic flame made a dramatic arrival in London on Friday when it was flown in by military helicopter and lowered to the ground by a marine commando a week ahead of the opening ceremony.

As the sun went down over the British capital, Royal Marine Martyn Williams abseiled from a Sea King helicopter hovering over the River Thames, carrying the Olympic flame to the ground in a lantern hanging from his belt.

The action film-style descent at the historic Tower of London began symbolically at 20:12 pm (1912 GMT), exactly seven days before the opening ceremony on July 27.

Williams, 23, who was injured in Afghanistan in 2008 but is now fit again, passed the flame to British athlete Kelly Holmes. The winner of the 800 metres and 1,500m at the 2004 Athens Olympics then used the lantern to light the Olympic torch.

The flame will spend the night locked up in the Tower of London, the 11th century fortress where Queen Elizabeth II keeps her ceremonial jewels and where the Olympic medals are also being stored for safekeeping.

It will then embark on a seven-day tour of the capital -- the culmination of an 8,000-mile (12,800-kilometre) relay around Britain and the Republic of Ireland.

London Olympic chairman Sebastian Coe said he was "delighted" to welcome the flame at the end of the 63rd day of the relay, adding: "It's made an extraordinary journey."

Mayor of London Boris Johnson said: "Tonight London becomes the first city in history to be entrusted three times with the sacred flame of the Olympics first kindled by the ancient Greeks.

"It will spread the crackling bush fire of Olympic enthusiasm throughout this city and this country.

"I pledge that we will keep that flame burning brightly."

Earlier Friday, before the flame reached the capital, police arrested a 17-year-old man after he tried to grab the torch from a female torchbearer while it passed through Gravesend, a town southeast of London.

The teenager sprinted out of the crowd toward the torchbearer and was grabbed by the security officers accompanying the torch.

The flame later travelled to Guildford, south of London, before being flown into the capital.

The torch will begin its tour of London in Greenwich on Saturday and will travel through every London borough, carried by 982 torchbearers, in the coming week.

Finally, the last torchbearer will light a cauldron at the opening ceremony in the Olympic Stadium, marking the official start of the Games.

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 chief organiser 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 1,200 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 an Olympic event, 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."

Asked whether he could wear Nike trainers, since Adidas is an official 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?"

Amid gripes about the Olympic security and transport the London mayor hit out at critics of the Olympics, saying Britain was about to stage the greatest show on Earth.

"Oh come off it, everybody -- enough whimpering," Johnson wrote in The Sun newspaper.

"Cut out the whingeing. And as for you whingers, put a sock in it -- fast."

AFP Photo/Carl Court