Glasgow's streets brought to standstill by 'Brad Pitt effect'

Through the window is another world: one of weary American commuters standing by a bus stop, a traffic cop in black leather jacket and peaked cap - and a tall man with light facial hair, a blue windcheater jacket and a million-megawatt smile. Ladies and gentlemen, Brad Pitt is in town.

The landscape is 16th Street and John F Kennedy Boulevard in Philadelphia, to be precise, where the streets are gridlocked with yellow taxis, blue Chrysler vehicles and blue and white police cars.

Cochrane Street, which runs parallel with Glasgow City Chambers, has been screened off at both ends and at every entrance by 8ft-thick black barriers guarded by polite American crew members, built like Fort Knox but with a ready line in polite patter: "Careful ma'am, you might just hurt yourself."

But the bar's elevated gantry offers the perfect view. At 8am it is being enjoyed by two Polish cleaners, who screech: "Look, look" and "Run, run". A blonde waitress is soon hyperventilating and shouting: "Oh my God, oh my God, oh my God: it's Brad Pitt." After the film star passes, she actually begins to physically shake for a few minutes. Forget Lynx, this is "the Brad Pitt effect".

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On the set of the 120 million movie, the cast and crew are a little less starstruck. Pitt arrives in a dark blue chauffeur-driven Jaguar and emerges clutching a thick copy of the script.

The director of World War Z, Marc Forster, takes up his position inside a black, open-sided tent in which the film monitors are set up. The continuity girl sits by his side with the script open in a ring-binder. The first shot of the day involves Pitt (who plays Gerry Lane, a UN specialist who is attempting to establish the cause of a virus which turns the population into zombies) sitting behind the wheel of a silver four-wheel-drive car, with his wife by his side and young daughter in the seat behind. The car is actually attached to the back of a truck on which a camera is set up, which tows the car while the action is filmed. A yellow cab is behind the car, and at one point a Philadelphia police officer on a motorbike glides past.

There follows take after take. It is said that the first day on a film set is the most exciting day of your life, and the second day the most boring. This, it must be said, is quite understandable.But for the myriad members of staff of Glasgow City Council this is clearly a day to remember, as they press themselves against the windows with camera phones at the ready.

Back in the bar, the girls have nipped next door to the sandwich bar to borrow two of their "I Love Brad" T-shirts and quickly squeeze into them before again taking up their positions at the windows. "How sad am I?" asks one. "This is my day off."

Just after 10am, the production halts for a coffee break and the crew take the opportunity to lower the large black drape that has been strung across the rooftops to ensure consistency of light during filming. Unfortunately, the heavy downpour earlier in the morning has left it sodden, and the waterfall is soon deposited onto the head of an unsuspecting security guard.

Once the coffee break is over, Mr Forster - who directed the James Bond film Quantum of Solace - returns to his little tent to hunch over the monitors once again. Pitt returns to the car and it continues: take after take.

Shortly after noon, Pitt breaks for lunch and comes up to shake the hand of the actor playing the police officer, much to the delight of Valerie McFarlane, a 59-year-old housewife who has travelled up from Troon to take pictures of the city for her daughters, who both live in America. "I wanted to say: 'Look, America has come to me'." Instead she finds herself a few feet away, albeit through a plate-glass window, from the biggest movie star in the world. "It's wonderful, just like when the golf comes to Troon."

Lunch, it appears, is a leisurely affair, as it is just after 2pm when Pitt returns to the set, his presence heralded by the appearance of his stand-in - a younger man but with the same blond hair, stubble and blue Barbour jacket - whose job is to stand or sit in his place during lighting and camera set-ups.

Outside the window, the crew have set up a bus stop and peopled it with commuters. A member of the continuity staff takes pictures of each one and later comes over to take the dark shades off one extra. It appears that he wasn't wearing them in an earlier shot and the shots need to match in the final edit.

Behind the black fabric barrier that the production has erected at both ends of Cochrane Street, a phalanx of photographers have set themselves up on ladders. One security guard is talking to another: "Them paps yesterday, they came into the production office asking to use the wi-fi! Incredible. Not on my watch, I tell ya."

For the next two hours Pitt sits behind the wheel of the silver 4x4 and watches as the same police motorcyclist drives past for take after take.

At 4pm, Pitt is courteous enough to reverse the car right up to the window of Committee Room No 9. He even gives us a wave. Unfortunately, word of the pub's legendary views has now spread to the point where the crew have to send in a production assistant to get members of the public away from the windows.

"Guys, I need you all to put the cameras down when we shoot - go crazy afterwards. You need to appear to be an ordinary customer if you are in the shot."

A window cleaner is sent over to clean the windows. "We are cleaning the windows so we can see you better," shouts the production assistant.

"Stand by."

"Turning over. Act nice and natural. Have a good time but don't stare at Brad Pitt!"

Maria Cristina Lai, from Vercelli in Italy, is asking the production assistant if Pitt will be coming into the pub to sign autographs. Unfortunately not, he explains. She sighs: "He is very beautiful."