Can this really be a British airport? As I stepped from the very first Heathrow Express train into Terminal 5 on Thursday morning, I marvelled at the soaring sense of space and style. A few minutes later, the sun rose through the clearest of skies to cast a suitably theatrical floodlight on the heavenly haven, which had just opened to British Airways passengers. As agreeably airy as an Asian airport, I wrote (sorry, the "a" key sticks on this keyboard).

I sought out attitudes to this altar to aviation. The first few views I canvassed were uniformly positive. "It's looking fantastic and working well," said one. "Brilliant – a great credit to everyone involved," added another. And the welcome lack of clutter won praise, too: "The shops aren't in your way, they're on your way."

This was not quite a representative sample. The first comment was from Mark Bullock, managing director of Heathrow; the second from Willie Walsh, chief executive of British Airways, the sole tenant of Terminal 5; and the third from Duncan Garrood, commercial director for BAA, the Spanish company that owns the £4.3bn building.

They had, I imagined, every right to feel smug that so complex a construction project had opened on time, on budget and on TV, courtesy of a line of satellite trucks and presenters. But at the time my tape recorder began to bulge with their self-congratulations, everything was beginning to unravel. The first flight, to Paris, departed on time – with all its passengers but with none of their checked baggage. Twelve hours and several dozen cancellations later, Gareth Kirkwood, director of operations for BA was telling travellers at the £4.3bn structure that they should forget about checking in baggage: "We always knew the first day would represent a unique challenge".

Understood: things go wrong. A decade ago, Denver's shiny new airport was delayed for over a year because of a malfunctioning baggage system. But instead of managing expectations, by cautiously explaining that teething problems could be expected, BA – and the airport's owner, BAA, hyped the project to the heavens.

"We are ready, so bring it on," said Willie Walsh in British Airways News. "Our customers will absolutely love T5 and our people will love working there." As I reported last week, he called the facility "an extremely sophisticated baggage system with a terminal built around it".

Even the Queen is quoted in the house journal, describing T5 as "A 21st-century gateway to Britain and the outer world". Yet for the many foreign visitors who spent unplanned hours at T5, "the outer world" must have seemed as distant as outer space.

The excuses provided when the terminal became paralysed by what were described as "problems associated with processing customers' baggage" were, frankly, lame. We had been told a week earlier that "The system has also been carefully designed to operate in two separate halves so that in the unlikely event one breaks down, the other will work as normal."

What do you think of it so far, I enquired of a lift full of weary passengers just arrived from Miami, "Rubbish!" they chorused. "We waited 20 minutes for the airbridge to be connected to the plane, then the baggage reclaim broke."

This terminal was conceived 20 years ago and building started six years ago. Nearly two years ago, BAA announced the date and even the time that it would open. For the past six months, British Airways has been conducting trials, involving thousands of pretend passengers (including me) and their pretend baggage. It beggars belief that that the airline had not deduced that its "state-of-the-art" baggage system might not survive contact with the public and trimmed its ambitious plans accordingly.

People are making comparisons between Terminal 5 and the Dome. That's unfair – on the Dome. I was at the much-maligned Millennium project on opening day. While 1 January 2000 wasn't the greatest day out I've ever had in my life, it delivered what was promised.

At 7am on Thursday, I asked Willie Walsh what surprised him most about Terminal 5 going live. "That the sun is shining". By the end of Day One, BA's chief executive may have been praying for fog, to obscure the national embarrassment that he helped to perpetrate.