London ( CNN ) -- The Olympic torch is set to make a dramatic entry to London Friday , descending via a 180-foot line from a helicopter to the historic Tower of London . The torch 's arrival in the capital begins the final week before the Games open and the final stage in its long journey . More than 10 million people have already lined the streets of more than 1,000 communities around Britain to see the torch , which has been carried by more than 7,000 torchbearers , Olympic organizers said . Nearly 1,000 more will carry the torch along nearly 200 miles of London streets over the coming week , before it takes a starring role at the opening ceremony at the Olympic Park on July 27 . Read about Greece passing the Olympic flame to Britain . Eighteen torchbearers will carry the flame on the final day of the relay , with seven of them traveling with it down the River Thames on the royal barge Gloriana , which played a central role in the Diamond Jubilee river pageant for Queen Elizabeth II . The torch 's arrival at the Tower of London on Friday evening promises to be eye-catching . A Royal Marine commando , carrying the flame in a lantern , will abseil -- the technique known as `` rappel '' in the United States -- 180 feet from a Royal Navy Sea King helicopter into the grounds , where London Mayor Boris Johnson will be waiting to greet it . The torch will be carried around the Tower , which dates back to the 11th century , before spending the night in the safekeeping of the Jewel House , home of the Crown Jewels . The buildup to the Olympics has been overshadowed by a security fiasco caused by the failure of contractor G4S to supply enough guards for the Games . 2012 Olympic flame lit in ancient stadium . But Johnson told CNN 's Becky Anderson that while London authorities are not complacent , he is confident in their ability to keep visitors safe . `` We do everything in our power to maximize security at the venues and that 's working well now -- the army , the military as well as G4S are providing very safe conditions on the site , plus there is a huge amount of work that nobody has seen involving the intelligence service , '' the mayor said . `` That 's something about an event like this -- you listen out for what may or may not be happening on the Internet , you try as hard as you possibly can to monitor the potential suspects . '' Johnson said it is impossible to guard against all `` unknown unknowns '' and that 's why strong security is needed at venues . `` At no stage can you guarantee that someone wo n't do something moronic , stupid , violent and tragic , not just in London but the whole of the UK is a potential target in this period , '' he said . But at the same time , he said , `` the intelligence is as reassuring as it could be under the circumstances . The threat level as far as we are aware has slightly come down in the last 12 months , but you can never be certain . '' Look at photos of the journey of the Olympic flame . Authorities said Thursday that an additional 1,200 British troops were being placed on standby for the Olympic Games . The company 's recruitment shortfall had already forced the government to call in 3,500 extra military personnel to help . Culture Secretary Jeremy Hunt , the minister in charge of overseeing the Games , said that there was no need to deploy extra troops but that putting 1,200 on standby means they can be moved within 48 hours rather than seven days if required . G4S has a Â£284 million ( $ 444 million ) government contract to provide 10,400 security staff for the Olympic Games , but only about 4,000 guards are trained and ready . It expects to provide at least 7,000 by the time the Games start , chief executive Nick Buckles told lawmakers earlier this week . Home Secretary Theresa May gave more details on how the fiasco unfolded in a letter sent to the head of Parliament 's Home Affairs Committee on Thursday . Although the Home Office did not become aware of the full extent of the shortfall until July 11 , G4S had alerted the government to `` scheduling problems '' affecting staff numbers on June 28 , she said . Once it became clear how large the shortfall would be , the government put its contingency plans into operation , she wrote . `` G4S will still be making a substantial contribution to venue security , '' she wrote . `` All G4S personnel working on venue security duties will have had training for the role they are undertaking , '' May added . The G4S recruits are supposed to perform tasks including venue perimeter security , such as manning X-ray machines , searching people , searching vehicles and operating closed-circuit television systems , the company said .
A Royal Marine commando will bring the flame from a helicopter into the Tower of London . Torchbearers will carry the flame along 200 miles of London streets this week . The Olympic Games open in the city on August 27 . The start to the Games has been overshadowed by a fiasco over security guards .