Protesters promise a baptism of fire for Terminal 5

In two weeks' time, the Queen will open Britain's biggest building project: the £4.3bn Terminal 5 at Heathrow airport.

Despite the deep-rooted problems at Europe's busiest airport, Her Majesty can expect everything to go smoothly on 14 March – partly because police will keep anti-expansion demonstrators well away, and partly because no passengers will be there.

A bigger challenge faces the airport operator on 27 March, when the building's sole tenant –British Airways – moves in many of its flights.

Channel 4's Dispatches programme raised concerns this week ranging from the efficacy of security searches to the number of flights to which passengers must be "bused" rather than boarding via airbridge.

Perhaps Ferrovial, the owner of Heathrow, had spies on hand at Beijing's new Terminal 3 yesterday to find out how to get things right. Passengers on the first BA flight from the new facility enjoyed a stylish and serene 21st-century creation. Will those flying in the opposite direction have the same experience at Heathrow?

Terminal 5 begins with a big advantage over the ragbag of facilities elsewhere at Heathrow; the sense of light and space is a vast improvement. Yet the new terminal will mean increased hassle for some passengers – even in terms of getting there. At present, Tube trains serving all four terminals arrive and depart every five minutes for most of the day. From 27 March, Terminal 4 and Terminal 5 will be served by alternate Piccadilly line services, doubling the waiting time.

And not all BA flights will switch over. During the summer, travellers on BA flights could find themselves arriving at, or departing from, any of the five terminals.

For many British travellers starting or ending long-haul trips at provincial airports, Paris or Amsterdam could offer quicker transfers than Heathrow.

Minutes count at Terminal 5. BA, whose current punctuality record is lamentable, is introducing a zero-tolerance policy that could hit passengers who are, by the airline's definition, running "late". The airline will deny boarding to anyone who fails to get through security at least 35 minutes before departure.

And all domestic passengers will have to get used to the idea that they are fingerprinted as they enter the "airside" area, and again before boarding their plane. Over the past few months thousands of travellers have acted as guinea pigs, testing the processes at the new terminal. One said: "It's a good job that T5 has great views – you'll have plenty of time to enjoy them while queuing."

Diary of a Heathrow activist

Richard George is a co-founder of Plane Stupid, which protested on the roof of Parliament

* Monday

I go to the rally at Westminster Central Hall and watch 3,000 people cheering. I also spend a lot of time watching the Greenpeace action at Heathrow which is fantastic.

* Tuesday

I'm nervous today. A lot can go wrong tomorrow and I'm not looking forward to spending time in a jail cell.

* Wednesday

I meet everyone at Parliament. We get inside by saying we want to watch a debate. We go up in the lift. I accidentally walk into a committee room instead of the fire escape. But finally on the roof we walk straight across. Now on the roof, I realise we will get away with this and then, as the banners go, I feel so elated. I watch how all the policemen in the courtyard turn around and watch how it all dawns on them. It's hilarious being up here. We manage to last until Prime Minister's Question Time, and then we hear Gordon Brown had to go out the back door. He even makes a comment and that's when we decide to hand ourselves in.

* Thursday

I walk out this morning after 13 long hours in jail. I meet up with everyone and look at the media coverage and we discuss what went well but also how we could have done things better. We are so excited and we feel like we're winning this. Now already 18,000 people have objected to the runway so we are getting somewhere.

* Friday

I'm back at work to face the music. I will remember this week for a long time. I have spent a week with my friends doing what I really care about so I wouldn't change anything about it.