Heathrow's expansion is just two years from completion. Mark Rowe takes a peek at this controversial, yet magnificent project

Between 4am and 5am on 30 March 2008, a British Airways flight, probably from the Far East, will land at Heathrow and become the first to decant its passengers into Terminal 5.

The new terminal will provide the airport with an additional capacity of 35 million passengers a year. British Airways, whose operations are currently split between Terminals 1 and 4, will move all of them to the new building, where it will be the main occupant.

The public inquiry into the project lasted almost four years, which made it the longest in British history, and the green light was finally given only in 2001. Since then, BAA, which owns Heathrow, has wasted little time. Construction of this new gateway to the UK began in 2002 and the structure was completed this autumn, including the façade of 5,500 glass panels, covering 30,000sq m.

Whatever the rights and wrongs of building T5 - local residents and environmental groups fought a dogged opposition campaign - the final result will be undeniably spectacular. The project, which is costing BAA £4.2bn, is one of the largest construction projects in European history (though it has not always been a happy one - BAA has faced strikes and protests over bonuses and compensation for the time it takes to reach the site). With a floor space of 260 hectares, T5 is about the same size as Hyde Park or 50 football pitches. It employs 6,500 construction workers and has used 80,000 tonnes of steel.

The public will have access to four levels of the new terminal, while baggage conveyors will run underground for more than 17km. The terminal will house around 140 shops covering 22,000sq m, which will provide 50 per cent of BAA's profits as it seeks to claw back its investment. "We're not a registered charity," Tony Douglas, T5's managing director, points out. "While we want a huge tick in the box that says 'public service provider', we're also a private commercial business, not a philanthropic one."

The main building is more than 400 metres long, while the satellite terminals, T5b and T5c (the former will open in 2008, the latter in 2011), are each as big as Terminal 4. T5's station will have two platforms for the Piccadilly Line, two for the Heathrow Express and a further two that may in the future link into the national rail network.

A defining feature of the new terminal is the single-span 176m roof (the largest single-span structure in the UK) and a pedestrian concourse that links the coach and train stations and car park to the building. The aim is to provide passengers with as smooth and stress-free a journey as possible. Extensive use of natural light will dilute what Mr Douglas described as the "horrid subterranean experience" of most airports and allow clear views of the runways. "So many airports put all sorts of bells and whistles in place but they forget the basics," he said.

The new terminal, designed by the Richard Rogers partnership, will dramatically alter the perception of visitors to Britain, who may ordinarily be forgiven for thinking that, upon arrival at Heathrow, they have landed in an airport designed by, and for, Dawn Man. "The central terminal area is not a happy experience," admitted Mr Douglas. "There is a significant gap between what the original terminals were designed for and what flows through them. T5 will present a first impression that speaks volumes about the UK. It is truly worthy of Brunel in its design. There are no internal columns. All other airports look the same and flying into them is a bit like Groundhog Day, but Heathrow will now have a signature skyline."