Gorgo
1961

What do you do when you find an enormous monster lurking in the sea off the coast of Ireland? Well, what you don't do (apparently) is either:
a. Kill it.
or:
b. Hand it over to the proper authorities for testing, in case its mother turns up and lays waste to London.
No, what you do is drag it all the way to the South of England, stick posters on the sides of every red London bus you can find, and exhibit the thing in a frankly shoddy-looking circus.
Because of course, that's what one-of-a-kind scientific discoveries are for, isn't it? Well it was in the 60s, anyway. There's not a dissenting voice to be heard (apart from a couple of potato munchers laying claim to it for Ireland - ha!) as captain square-jaw and his jaunty-hatted mate set sail for good old blighty with their find in Gorgo, despite the monster having devastated a small fishing village and apparently been responsible for a major undersea earthquake. Bizarre.
Anyway, that's what happens at the beginning of Gorgo - unfortunately, yes, the British answer to venerable Japanese export, Godzilla.
Of course, no sooner has the sad-looking monster been put in its electrified pit for people to laugh at (why do they always laugh? They've paid good money to see it), than mum turns up - ten times the size and obviously on her monthlies.
She battles her way through an enormous amount of Royal Navy stock footage (the same guns go off again and again and again) as the Admiralty show a remarkable disinterest in the gigantic, seemingly indestructable beast (of course, that could be down to bad acting).
Once Britannia has shown it doesn't rule the waves any more (there's not a mark on mum despite the stock footage barrage), it's time to get serious as she nears London - "Send for the river patrol!" (I kid you not).
The River Patrol are even worse than the Navy (surprisingly) and only manage to set fire to the Thames (and a couple of Teddy Boys for good measure). Now it's time to "Send for the army!"
They're not happy though, having been told that "atomic bombs can't be used in any built-up area". So instead, everyone panics, despite being told not to. Mum wades into Tower Bridge, and follows up by dropping Big Ben on a group of soldiers (although to be fair, they'd already made a bit of a mess of it by firing rockets at the clock).
As the people panic even more, we're treated to the same scenes of milling about, except reversed - hence the ads for XULUD paint. Next stop Picadilly Circus - "there's no telling where this thing will turn next!" says an army boss - come now, surely there's loads more tourist attractions she can waste?
But no - not only does mum not stamp on an annoying reporter who's been giving us a particularly pointless rundown of all her activities, but she also avoids twatting the annoying child who somehow got attached to the baby monster at the beginning. So the film ends on positive note - London flattened, mum and kid reunited, and no-one arsed to try and stop them.
"They're going back now... back to the sea..."
Ready for Gorgo 2? Unlikely....

Gorgo (1961)
Director: Eugène Lourié (as Eugene Lourie) Writer(s): (WGA) (in credits order) Robert L. Richards (screen story) (originally as John Loring), and Daniel James (screen story) (originally as Daniel Hyatt), Robert L. Richards (screenplay) (originally as John Loring,) and Daniel James (screenplay) (originally as Daniel Hyatt)
Cast: Bill Travers - Joe, William Sylvester - Sam, Vincent Winter - Sean, Christopher Rhodes - McCartin, Joseph O'Conor - Professor Hendricks, Bruce Seton - Professor Flaherty, Martin Benson - Dorkin, Maurice Kaufmann - Radio reporter, Basil Dignam - Admiral, Barry Keegan - Mate, Tommy Duggan - First naval officer, Howard Lang - First colonel, Dervis Ward - Bosun, Róbert Arnfinnsson - Gudmundur, Gunnar Eyjólfsson - Ragnar, Nigel Green - Bulletin Announcer, Lawrence W. Schneph - US Drunkard, John Teasy - Bob