Heathrow Airport's controversial Terminal 5 is set to be opened by the Queen in a ceremony involving hundreds of airport and construction workers
The £4.3bn terminal offers extra passenger capacity although the number of flights will not increase after it opens for business on 27 March.
Operator BAA says it will "transform" the level of service at the airport.
Environmental and residents groups who have opposed it say it will lead to more flights, noise and pollution.
Security alert
The opening follows a major security alert at the airport on Thursday after a man with a rucksack scaled the perimeter fence and ran into the path of an aircraft.
The man was arrested and a controlled explosion carried out on his rucksack. Police said the incident was not terrorism-related.
The Queen, who in 1955 opened the airport's first terminal building, what is now Terminal 2, will be accompanied by the Duke of Edinburgh.
The royal couple will be met on the new departures concourse by Sir Nigel Rudd, chairman of BAA, which has funded the terminal.
Also present will be Transport Secretary Ruth Kelly, Rafael del Pino, executive chairman of BAA's parent company Grupo Ferrovial, and British Airways chairman Martin Broughton.
Along with 800 invited guests, including hundreds of airport and construction workers involved in the project, they will listen to a specially-commissioned piece of music performed by a 30-strong choir.
Some 60,000 people have worked a total of 100 million man hours to build Terminal 5 since construction began in September 2002.
Built on the site of a former sludge works at the western end of the existing airport, Terminal 5 has been designed by 2006 Stirling Prize winners Rogers Stirk Harbour and Partners.
Its construction has involved diverting two rivers, building what is claimed to be the UK's largest free-standing building and tunnelling 13km for rail and baggage links.
The complex includes 50 new aircraft stands, which will rise to 60 by 2010, two satellite buildings, one of which is still to be completed, rail links to London Underground and the Heathrow Express, and a new multi-storey car park.
Friday's official opening is of the project's Phase 1, including Terminals 5A and 5B. Phase 2, which adds Terminal 5C, is set to open in 2010.
Sir Nigel said: "From every perspective, this is a landmark project and I am proud to think that Terminal 5 has become a model construction project, setting new, higher standards for an industry around the world."
BAA says it will simplify the process of checking in for flights with online check-in, fast baggage dropping facilities and state-of-the-art baggage handling.
The first passengers will start using Terminal 5 in a fortnight when they step off a BA flight from Hong Kong.
The terminal will be solely for the use of British Airways for international flights and to and from Manchester, Newcastle, Belfast and Scottish airports.
'Broken promises'
Virgin Atlantic has complained that BA will be the only airline to benefit from the new terminal.
Director Paul Charles said: "This is a great new building, there's no doubt about it, and it may be a wonderful new piece of infrastructure and architecture, but it doesn't do anything for most of the airlines that operate at Heathrow.
"This is a gift for BA. They've been gifted terminals before, such as Gatwick North and Terminal 4.
"Here they are getting Terminal 5, and fundamentally it's a great place to shop but it may not be a great place to travel from."
However, BA chief executive Willie Walsh, said it was not unfair for the airline to have sole access to the terminal.
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