By Joe Boyle
BBC News, Heathrow Airport
BA staff were on hand to explain the new procedures...
As Heathrow Airport struggles to return to normal after an alleged terror plot was prevented, many passengers are still experiencing cancellations, delays and confusion.
The first time you realise Heathrow is not running as normal is when you get in the lift at the train station - it is not going to the departures hall.
A well-dressed airport official politely explained: "There are too many people in departures, so this lift can only go to arrivals."
In the arrivals hall, more sets of lifts are patrolled by eager airport staff. "These lifts are only going down, sir", said one. "The only lifts to departures are in the car park."
An unusual introduction to the world's busiest airport. But in the lift from the car park, passengers find time for some good-natured banter.
One middle-aged woman explains to her co-travellers that she has already been subjected to two cancelled flights in Copenhagen. Another explains how this is his third trip to Heathrow in the last two days.
Cups of coffee
The departure hall at Terminal 4 has largely moved outside - with huge, white marquees offering shelter to hundreds of expectant travellers.
Cups of coffee are handed out by the legions of British Airways staff drafted in to help the crowd.
...and to hand out pink umbrellas
Dressed in fluorescent yellow jackets, the BA workers clutch megaphones and shout out flight numbers. Dozens of passengers obediently shuffle into the terminal building when their number is called.
The rain begins to fall and BA personnel are quickly on hand to supply pink and black umbrellas to their stranded customers.
Despite the evident inconvenience, the mood is generally calm and most people seem resigned to waiting.
Michael Sinclair - who is waiting with his 14-year-old granddaughter, Cleagh - summed up the mood when he said: "You can't really blame them, they are taking extra security measures."
He added: "Right now, we are very patient. We were told to turn up four hours before the flight was due, and that's what we have done.
"We're pretty confident that the flight will go."
The sheer scale of the difficulties the airport faces are evident inside the terminal building, where queues of bored-looking passengers snake around the departures hall and airline staff continue to hand out the now-ubiquitous clear, plastic bags for hand luggage.
One airline worker, with the Qantas logo on his ID badge, said that he had been drafted in from Australia to help put into effect the new security measures.
He said passengers were still being extremely good natured about the delays and were just keen to understand the security situation and deal with it in the best way possible.
Passengers crowded into marquees and were given tea and coffee
Travellers in the departure hall told of the confusion they were experiencing with their flights.
One family from Hyderabad in India said they were on their way to Zurich but the flight had been cancelled.
Ramesh Gambhir said: "We've only just found out that our flight has been cancelled and now we don't know what we are going to do."
Their story was far from unusual in the chaotic terminal building.
Back outside, with the rain coming down harder, hundreds of passengers continued to endure the weather and the wait.
Pete Bectkmans, a 24-year-old business student, said: "I guess if our flight is cancelled again, we will just have to come back and try another day."