Gorgo

Gorgo is a 1961 British monster film directed by Eugène Lourié and featuring special effects by Tom Howard, and starring Bill Travers, William Sylvester and Vincent Winter. In the film, after an undersea volcano sends tremors throughout the Atlantic, a prehistoric creature is released from under the sea. The crew of a salvage vessel capture the giant amphibious creature and take it to London for public exhibition. It results in the creature's much larger mother invading London in search of her offspring, causing catastrophic destruction across the city in the process.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.