We listen carefully to Tony Douglas, T5's managing director
Tony Douglas is used to a struggle, inured to disappointment. He is, after all, an Everton fan. And in spearheading the £4bn Terminal 5 project he faces a task even greater than Everton's annual fight to avoid relegation. And while most Everton fans delude themselves that theirs is still a big club, Douglas really is at the top of the league: T5 is Europe's largest construction project.

"It is very much a bet-the-farm type of venture," concedes the remarkably energetic Douglas. Airports operator and T5 client BAA has a market value of about £5.5bn, so BAA is placing a great deal of trust in Douglas to deliver the scheme successfully.

The risk profile of T5 is different to any other project BAA has built. Its other jobs were smaller, so during an economic downturn could be delayed or rescheduled. In a scheme of this size, however, the programme has to be exact to keep costs down, and business concepts such as just-in-time delivery have to be used. "In reality, once the starter's pistol's fired on T5, it's game on until it is completed – so there is no opportunity to do anything other than the programme," says Douglas.

Douglas turns to his favourite analogy – football – to insist that BAA is match-fit for the equivalent of the World Cup final: "It has been a function of practising for the big match. In lots of the other big projects we have been innovating in terms of process and developing partnerships. This is the big one."

Douglas talks excitedly about how BAA has spent the past decade turning suppliers into partners. This is not mere semantics, he insists. The T5 agreement means that, if something goes wrong, BAA will accept financial responsibility for it. This means that contractors are not continually watching their backs when problems occur. Instead, they use what Douglas describes as their "intellectual horsepower" to solve the problems.

Douglas points to how quickly problems were fixed at T5's control tower as evidence that the approach is more sophisticated than the traditional risk model. He adds: "The notion that I could chase the contractor for £10m might – in the bravado-laden world of macho, old-fashioned contracting – feel good. In reality, if litigation leads to me holding up a day of Heathrow airport's operations, it's compounding the mistake."

T5 has to be delivered on 31 March 2008. That is the day BA is to move all its operations into the terminal. There is no margin for error. Douglas argues that any delays would not just harm BAA and BA, but the entire UK economy. The airport handles 64 million passengers a year, Heathrow is Britain's biggest port, its single biggest wealth creator and the "gateway to Europe", says Douglas. Multinational companies set up their headquarters or main support offices in London over Frankfurt and Paris because of the ease of access to the rest of the world. If T5 is delayed or, worse still, fails, these multinationals might make their way to the departure lounge.

The word ‘terminal’ is misleading. By itself it would be the fourth biggest airport in Europe

"Very simply, Heathrow will just run out of space to meet demand. Pretty much by 2010, the game would be up," says Douglas. For the past three decades, air travel has grown at a rate of 3-7% a year.

The new terminal will calm these fears, because it is just so enormous. "The word 'terminal' is mildly misleading," says Douglas, "By itself it would be the fourth biggest airport in Europe. There would only be Heathrow, Schiphol in Amsterdam and Frankfurt bigger. And it comes complete with all this infrastructure, such as the new spur road off the M25 and extensions to the Heathrow Express and the Piccadilly Underground line."

Douglas is right: this is no mere terminal. He describes the floorplate as being the size of 50 football pitches. It will have more than a third of the amount of retail contained in Bluewater, the giant shopping centre in Kent. BAA is in early talks with tenants to occupy space at T5. And it is little wonder that they are already queuing up, as the shops located in Terminal 3 break just about every international trading record. For example, there are more Rolex watches sold in T3 than anywhere else on the planet.

T5 is a true mixed-use scheme. It will also include a 600-bed five-star hotel, a 4000-space car park and a massive energy centre providing heating, cooling and phased power.

Putting together these complex pieces is costly and timely, so Douglas is relieved that, with 35% of the project complete, he is on schedule to complete his mission. "If you had offered this to us 20 months ago, we would have snatched your hand off with glee," says Douglas – before switching back to John Motson mode, "It's kind of like buying a 1-0 win, or a 1-1 away-from-home against Real Madrid – before kick-off you would have it; it would be a great result."

A great result maybe, but there is 65% of the league programme still to go, and in a project of this size there will inevitably be own goals and dropped points. Almost Arsene Wenger-like, Douglas has warned his team against "foolhardy" complacency.