Opened in 2008, the main building in the complex is the largest free-standing structure in the United Kingdom.

The building cost £4 billion and took almost 20 years from conception to completion, including the longest public inquiry in British history.

Richard Rogers compared his design to the Centre Pompidou, an earlier project that has similar flexibility in its use of space.

[4][5] A public inquiry into the proposals began on 16 May 1995 and lasted nearly four years, finally ending on 17 March 1999 after sitting for 525 days.

[9] In November of the following year, work started on the steel superstructure of the main terminal building.

In March that year, the sixth and final section of the main terminal roof was lifted into position, and in December the building was made weatherproof.

The roof could not have been lifted with conventional cranes because it would have vertically intersected with the airport's radar field.

[10][11] Over 15,000 volunteers were recruited for a total of 68 trials lasting from September 2007 until March 2008 to test the operational readiness of Terminal 5 prior to its opening.

Used by British Airways (and now IAG (Iberia)) as well as American Airlines (OneWorld Partner), the terminal opened for passenger use on 27 March 2008, with flight BA26 from Hong Kong its first arrival at 04:50 GMT.

On the day of opening, it quickly became apparent that the new terminal was not operating as planned, forcing British Airways to cancel 34 flights and suspend baggage check-in.

[16] The difficulties were later blamed on a number of problems with the terminal's IT systems, coupled with car parking.

[18] Four months after opening, British Airways launched an advertising campaign to assure the public that things were working normally.

The site was previously occupied by the Perry Oaks sewage works and an area of smallholdings called Burrows Hill Close Estate, and is east of the M25 motorway; see also Heathrow (hamlet).

This was a complex scheme, which involved not only the re-routing of the two rivers but also the realignment of the A3044 dual carriageway and Western Perimeter Road.

[26] Its four storeys are covered by a single-span undulating steel frame roof, with glass façades angled at 6.5 degrees to the vertical.

Departing passengers enter the departures level on the third floor by lift or escalator from the interchange plaza.

Upon entering the departures concourse, passengers see views across Heathrow and the surrounding area, and are in a space that is unobstructed to the rising roof above.

After check-in and security screening, the airside departure lounge also provides views across the airport, its runways and beyond.

British Airways maintains offices overlooking the main Terminal 5 passenger handling areas, designed so that staff can have, in the words of Aviation Transport Weekly, a "visual connection to customers".

[11] There is also the potential for an additional satellite building, T5D, to be located to the east of T5C, as displayed in Heathrow's Capital Investment Plan for 2009.

[11] At the time of its design Terminal 5's proposed height was so tall that it would have blocked runway views from Heathrow Airport's then control tower.

A 2.4-mile (3.9 km)-long personal rapid transit system, known as the Pod, links the nearby business car park and the main Terminal 5A building.

The Pod system is operated landside with a fleet of battery-powered, driverless ULTra vehicles running on an elevated and at-grade segregated guideway.

[citation needed] An underground automated people mover (APM) system, known as the Transit, is used to transport passengers between the 5A, 5B and 5C buildings.

The Transit uses Bombardier Innovia APM 200 vehicles and operates exclusively airside, and is thus only available to passengers and other authorised personnel.

Passengers descend to the station via a pair of escalators "thought to be the largest in Europe in an open environment".

A proposal for the construction of a Western Rail Approach to Heathrow, a railway link connecting Heathrow Terminal 5 to the Great Western Main Line, was suspended in 2020 pending a satisfactory business case and funding agreement.

This link would allow rail services to continue westwards from Terminal 5 to serve stations in the West of England.