Don't worry, you don't have helicopters with global terrorists crashing on this bridge everyday. And even if it happens, James Bond is somewhere around, so it's not that bad.
Use Westminster Bridge if you are having an appointment with British secret service official, like "Rogue Nation's" Lisa. Or just walk and enjoy the great view on Thames and Houses of Parliament.
It's still there, don't believe this another terrorists-attack-a-big-city action movie, that will be released this year.
In Woody Allen's "Match Point" Chris uses this bridge to throw away evidences of his murder. But it's still a very good bridge, see it.
Nice bridge to have a romantic walk like Dustin Hoffman and Emma Thompson in "Last Chance Harvey".
Cillian Murphy's Jim is totally alone on Westminster Bridge. Because zombie apocalypse, you know. But in real life this iconic bridge is much more crowded.
And last but definitely not least, one of London's landmarks in the film about one of the most famous Brits. In Guy Ritchie's "Sherlock Holmes" Robert Downey Jr's Holmes have a final fight with a villain on the top of Tower Bridge, still in construction.