The three-hour showcase created by Oscar-winning "Slumdog Millionaire" director Danny Boyle takes spectators on a journey from Britain's idyllic countryside through the grime of the Industrial Revolution and ending in an explosion of pop culture.

Watched by 60,000 people at the main Olympic stadium built in a run-down part of east London and a global audience of more than a billion, the event will have passages described by British Prime Minister David Cameron as "spine-tingling".

The spectators will be urged to join in sing-a-longs and help create spectacular visual scenes at an event that sets the tone for the sporting extravaganza, when 16,000 athletes from 204 countries share the thrill of victory and despair of defeat with 11 million visitors.

The Games will also answer the question on Britons' lips -- were seven years of planning, construction and disruptions, and a price tag of $14 billion during one of the country's worst recessions, actually worth it?

"There is a huge sense of excitement and anticipation because Britain is ready to welcome the greatest show on Earth," said Cameron. "This is a great moment for our country so we must seize it."

There have, however, been bumps along the way.

Media coverage was until recently dominated by security firm G4S's admission that it could not provide enough guards for Olympic venues. Thousands of extra soldiers had to be deployed at the last minute, despite the company's multi-million-dollar contract from the government.

Counter-terrorism chiefs have played down fears of a major attack on the Games, and Cameron said that a safe and secure Olympics was his priority.

"This is the biggest security operation in our peacetime history, bar none, and we are leaving nothing to chance."

Suicide attacks on London in July, 2005, killed 52 people. This year the Games coincide with the 40th anniversary of the 1972 Munich massacre when 11 Israeli Olympic team members were killed by Palestinian militants.

Heavy traffic in central London and severe delays on Britain's creaking train system have added to the grumbling.

A series of doping scandals have tarnished the Games' image in the buildup, with at least 11 athletes banned, and Greek triple jumper Paraskevi Papachristou became the Olympics' first "twitter victim" when she was withdrawn from the team over tweeted comments deemed racist.

An early diplomatic faux pas, when the flag of South Korea appeared at a women's soccer match between North Korea and Colombia, prompted fuming North Korean players to walk off the pitch and delayed kick-off by more than an hour.

SATANIC MILLS

All of that is likely to be forgotten as attention around the globe turns to the opening ceremony, which begins at 2000 GMT and ends more than three hours later.

While Boyle has urged the 10,000 participating volunteers and large crowds at rehearsals this week to keep the show a secret, some elements are already in the public domain.

Titled "Isles of Wonder", it opens with a recreation of bucolic bliss, complete with fields, hedges, sheep, geese, a shire horse, shepherdesses and even a game of village cricket.

The mood then darkens as "England's green and pleasant land", from a poem by William Blake, makes way for the sooty chimneys and smoking steel works of the "dark Satanic Mills", evoking the 19th century urban settings of Dickens.

Stirring music from Britain's past and present provides the soundtrack, which comes to the fore in the latter stages with a psychedelic celebration of pop culture including songs, sitcoms and cinema classics.

Cyclists with illuminated "wings" circle the arena, creating a stunning effect for cameras suspended from the stadium roof.

Boyle's ode to the National Health Service, a politically charged topic in Britain where people are emotionally tied to the ideal of a welfare state, may make less sense to people watching from afar.

But a closing performance by ex-Beatle Paul McCartney should have global appeal for a ceremony that will contrast sharply with Beijing's tightly choreographed, large-scale version.

Boyle had 27 million pounds to spend on his spectacular, well under half the amount estimated to have been spent in China in 2008.

There are still plenty of secrets, including who will have the honour of lighting the Olympic cauldron, the moment symbolising the opening of the Games and ending the Olympic torch's 8,000-mile (13,000 kms) journey the length and breadth of Britain.

On Friday, the torch made its way up the River Thames aboard the royal barge Gloriana, which was used in Queen Elizabeth's Diamond Jubilee in June.

The 86-year-old monarch will be in the crowd, along with U.S. First Lady Michelle Obama and a host of dignitaries and celebrities.

Showers forecast for London after a week of sunshine are expected to clear in time for the ceremony, according to Britain's Met Office.

In his final news conference before the Games, International Olympic Committee president Jacques Rogge said a crackdown on dopers had proven a success with more than 100 athletes caught for doping violations in the months leading up to the Games.

"This is a good sign for the fight against doping," Rogge said. "This is proof that the system is working and is effective."

ARCHERY WORLD RECORD

South Korean men's archers set the first world records of the Games, the team totalling 2,087 for 72 arrows at Lord's Cricket Ground. Im Dong-hyun, who suffers from severe myopia and just aims at "a blob of yellow colour", broke his own 72-arrow world record with a score of 699.

The Games' first medals will be decided in the women's 10 metres air rifle final on Saturday with the big action coming in the men's road race where world champion Mark Cavendish is favourite to become Britain's first gold medallist.

In the evening, Americans Michael Phelps and Ryan Lochte are scheduled to line up for a classic confrontation in the men's 400 metres individual medley final.

Phelps, swimming in seven events after winning a record eight gold medals four years ago in Beijing, is bidding to become the first man to win the event for three Games in a row.

However, he was beaten by Lochte in both last year's world championships and this year's U.S. trials.

"This is going to be a special race," said Gregg Troy, head coach of the American men's team. "I can't imagine a better way to promote our sport than a race like this on the first day." (Additional reporting by Stephen Addison, Gene Cherry, Guy Faulconbridge, Vincent Fribault, Peter Griffiths, Sara Ledworth)

• A Permanent Economic Emergency