By Tom Symonds BBC transport correspondent

Passengers will start using the terminal on 27 March

A new era for Heathrow is beginning with the opening of Terminal 5, the new home of British Airways' operations, 18 years after it was first proposed.

It was in May 1995 in a ballroom at a hotel airport that arguments began about whether Heathrow should get its fifth terminal.

It was to become Britain's longest planning inquiry, but finally in 2001 the government gave permission to build Terminal 5 (T5).

The alliance of campaigners opposed to expansion was furious.

The terminal expands the capacity of Heathrow by 30m passengers

The government had gone back on a recommendation from the Terminal Four inquiry that the growth of the sprawling airport should end there.

But Heathrow's owner BAA, and the airlines operating out of the airport, insisted that it was Britain's premier hub for air travel, and warned that it was bursting at the seams and badly in need of expansion.

There were 'conditions' for going ahead with T5; a cap on flights of 480,000 a year, limits on noise, and restrictions on car-parking.

Mammoth building task

They weren't enough for the protestors, but regardless, the construction of the glittering new airport building began.

It was a mammoth task, not confined to the building itself.

Two rivers had to be diverted, and extensions were dug to London Underground and Heathrow Express rail lines.

A new road tunnel was bored, and a taller Control Tower erected to give better oversight of the bigger airfield.

Now Terminal Five stands huge, and strangely distant, at the far end of the airport, its size only apparent when you arrive at its doors, as passengers will do on March 27th.

Advantage BA

British Airways, which has the run of the place, believes T5 will transform its passengers experience of air travel.

BAA hopes 80% will check-in online or at computer terminals

Its rivals grumble that yet again, BA has been handed advantage on a platter.

The promise to passengers is that T5 will transform their experience of air travel, and banish 'Heathrow Hell' for good.

It is hoped 80% of passengers will check-in online or at computer terminals in the vast departure area.

Bags are dropped at desks nearby, and security is just beyond, expanded following the terror scares of recent years.

Another big idea is that no passenger should have to walk more than 5 minutes to reach their aircraft.

There should be no more frantic sprints along endless corridors.

This has been achieved by having the aircraft pull up at air bridges connected to the main building itself.

Terminal Five, BAA is eager to point out, has been completed on time and on budget, using entirely private money.

More space

So what has that money really bought?

Certainly space. Floor space within the terminal for passengers, freeing up crowded buildings such as Terminal One.

The extra departure gates will make aircraft operations easier, especially when things go wrong, which currently leaves planes queuing to load and unload.

The road traffic to the central airport area should ease a little, as a proportion of it heads instead to T5 to the west.

For British Airways, handling baggage should be easier.

A state-of-the-art system of conveyor belts, computerised baggage trucks and a new reclaim area will help improve the airline's reputation for losing its passengers luggage.

The development also buys BAA time.

The terminal expands the capacity of Heathrow by 30m passengers, but they won't all come on day one.

So the company can begin its next plan, knocking down Terminal 2, and building what it calls Heathrow East.

The airlines displaced will take BA's place in T1 and T4.

But T5 doesn't solve the airport's biggest problem.

Runway pressures

The pressure on its two runways.

Planes can take off and land every minute, such is the frantic pace of air traffic.

It is claimed by the airport that the new terminal will not radically increase flight numbers, despite the increase in passenger numbers.

This is said to be because bigger aircraft are being used, including the giant Airbus A380, due to begin UK operations with Singapore Airlines next week.

Environmentalists don't believe that for a minute, and local campaigners have tracked the growth of the Heathrow operation in the years since T5 was first agreed.

A consultation has been carried out into a third runway, north of the airport, and it seems likely the government will go ahead with this proposal too - triggering years of protest from green campaigners.

And so the cycle continues.

Demand for a bigger Heathrow, expansion to provide it, followed by more demand.

It must all seem very strange for the Queen.

After all, when she opened the first terminal building at Heathrow half a century ago, in 1955, airport travel was still in its infancy.

Now it is clear that it was just the start of something very big.