(1971, Jean Paul Belmondo, Omar Sharif) “I saw a film many years ago which featured both interior and exterior shots of an Athens trolleybus,which I think would have been an Alfa Romeo vehicle. A taxi driver is actually told - 'Follow that trolleybus!' ” (suggested by Alan Sinclair). Many thanks to Barry Spence who identified the movie.
Belmondo is the villain of the title, Sharif the corrupt police officer in a movie shot in Athens. The stunt work is excellent, including a riproaring car chase through busy streets that lasts close to ten minutes. Of more relevance to this website is a second chase sequence that involves Belmondo, a trolleybus, a diesel bus, a coach and a lot of clambering about! Several other Greek buses not involved in the action also pass in the background. I'm not expert on Athens buses, so any help with identification is welcomed!
The car chase sequence starts at the port, where these buses are seen outside:


As the chase begins, numerous buses are glimpsed:


In the second sequence, Belmondo escapes from the police initially by boarding an Alfa Romeo 140a trolleybus, fleet number 1012:


The police are following, and in heavy traffic Belmondo clambers out of the trolleybus window, across to a bus passing in the opposite direction. This is a Leyland Royal Tiger Worldmaster with Biamax body.


It's at this point that Sharif's character commandeers a taxi!

The chase is on, and Sharif uses the taxi door to try to push his quarry off the bus:


Belmondo escapes again, by clambering onto a passing coach, just as more police cars arrive. Note the camera mounted on the side of the bus creeps into shot as Belmondo climbs the ladder on the back of the coach!


Sharif switches back to a police car as another Alfa Romeo trolleybus and two diesel buses pass:

But Belmondo is away, on the coach roof. A Mercedes coach passes in the other direction:

We never see the coach in full, even as Belmondo jumps off: