Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a British spy movie, one in a series of three that star secret agent Dick Barton, a sort of pre-curser to James Bond. This one involves a group of terrorists who are killing entire villages of people in England with a new weapon that uses sound waves.
Dick Barton (Don Stannard) is captured while snooping around. The head bad guy tells his henchman Fouracada (Sebastian Cabot) to kill him and his sidekick Snowey (Bruce Walker) any way he wishes, making sure they don't escape. Instead of killing them the smart and easy way, with his revolver, just shooting them in the head, Fouracada decides to get clever. Earlier he thought it was clever to tie them up in a room with a candle then turning on some gas to blow them up when the gas hit the flame. But that didn't work either. This time he locks them in a room at the aquarium full of snakes in glass terrariums. He even brags to Barton how smart and creative he is in killing him with snakes. (I beg to disagree.) Then Fouracada shoots the terrariums from a window to the outside, and the snakes escape. He calls that he's releasing a Black Mamba and a Cobra as he keeps shooting. Somehow he manages to squeeze about ten shots out of his six-shooter. Barton tells Snowey that the snakes are all poisonous, but the labels on the snake cages say otherwise. One identifies the snake as an Imperial Boa, and the other as an African Python, two non-venomous snakes. Fouracada leaves, like all dumb movie villains, leaving the snakes to crawl very slowly (a crawling snail would beat them) towards Barton and Snowey who begin to give up hope. (It would be very easy for them to simply step over and avoid the ponderous snakes but that wouldn't be "dramatic.") But just as the snakes are closing in on the men (they'll be there in a couple of hours at most) Deus ex Machina lowers a rope from a skylight to save the men. They climb up the rope only to be shot at again on the roof by Fouracada. Barton dodges the bullet and pushes Fouracada through the skylight into the snake room where we last see him lying unconscious with snakes crawling next to and on top of him, ready to bite him savagely, in maybe an hour or two.
As far as I can tell, all of the snakes are Boa Constrictors - very nice-looking dark ones, possibly Argentine Boas.
You can watch the whole movie and read a synopsis of it at the SilverScream. the scene starts at about 54:18.