It was inconceivable that everything would go smoothly for British Airways and BAA on the opening day of Terminal 5, but no-one expected the shambles of today's operations.

Journalists, myself included, were braced for the chaos that a "Flash mob" of Plane Stupid protesters could bring to the Arrivals Hall mid-morning, or the security alerts that were anticipated to dog such a high profile event, but no-one expected this.

When the first flights took off early this morning, everything was going smoothly at Terminal 5. The excitement among BA officials, who chatted incessantly into radios and mobile phones around the terminal, was palpable. It seemed as if finally BA might shake off the bad press that came with the strike threats and Terminal 4 baggage backlog earlier this month.

Finally the national carrier and self-proclaimed "world's favourite airline" had something to be proud of.

In the Concorde lounge I saw the senior BA executive Tiffany Hall purveying the scene of relative calm in the Departures Hall with noticeable pride over a cup of coffee, and her boss Will Walsh, chest puffed out, being interviewed by television crews in the check-in area. She told me the terminal was quiet because only 10,000 passengers were expected to use it today - a fraction of the terminal's full capacity.

But sadly for BA it wasn't to last.

What started the toppling of dominoes for BA isn't clear, but for us departing passengers it was the faulty screens that caused early confusion.

The information boards in Departures gave a glowing indication of flight punctuality but turned out to bear little relevance to what was going on at the gates.

At gate B44, where I was sent for my 8.55am Brussels flight, the departure board flitted between my flight and another to Munich.

Another nearby board showed the wrong time, and BA staff grew gradually more fractious as the passengers did.

What turned out to be holding us up was a missing fluorescent wasitcoat, known as a tabbard in the trade. It must be worn by airline staff escorting passengers to the steps of an aircraft (the air bridge wasn't working). Hard to believe that for the 100-odd passengers on my flight it was a missing jacket that was the straw that broke the camels back.

It got worse for BA - the baggage system that it had extensively tested and bragged of handling 12,000 bags an hour turned out to be incapable of handling the bags of some 10,000 passengers in a day.

When I walked through the baggage hall this evening, after a three-hour delay to my flight, abandoned cases were strewn around the hall - mingled with litter and dozing passengers - it took the shine off the gleaming baggage belts and glistening floor.

When I boarded my return flight to Heathrow the captain told us: "It looks like it hasn't worked out brilliantly at Terminal 5", "that's an understatement" muttered my frazzled neighbour. "It's the first flight of the day for myself and my co-pilot Lars," he added, "so we're not sure how chaotic it'll be when we get there."

I felt like we were heading into the gates of hell. But a harder pill to swallow? While queued up to board our delayed flight in Brussels we were given little blue BA-branded carrier bags - a gift, the cheery steward told us. Inside was a tiny box of two chocolates and a leaflet about Terminal 5. On the front it said: "So calm, you'll just flow through".

To comfort BA one might say, "Oh well, tomorrow's another day", but with announcements ringing out across the terminal now that passengers with hold luggage are no longer being allowed on flights, I think that phrase will only instill fear into the BA executives who are in for a second sleep-deprived night.

Times recommends

• The smart guide to travel blogging
• 30 top takes on New York
• Europe's 20 best Christmas markets 2009