The whole place is completely sealed. It's as simple as that.
6 seconds sound clip from the The Abominable Dr. Phibes movie soundboard.
You can hear this line at 01:03:24 in the Blu-ray version of the movie.
Quote context
[...]
- A brass unicorn has been catapulted across a London street and impaled an eminent surgeon.
- Where are you off to now, Trout?
- Evening, Constable. Everything quite normal?
- Good.
- The whole place is completely sealed. It's as simple as that.
- Simplicity isn't exactly the word I'd use in dealing with this man, Inspector.
- I've got half the Yard, sir, plus some of the local boys and a small mobile unit here.
- I've got cars all round the place here, here, and here and, of course, some plainclothes men.
[...]