Matchbox Sea Kings, I remember these from when I was a kid. I got these for a tenner, so at £2 a pop that seemed a bargain. I don't know what scale they are meant to be (knowing these old die-cast they probably had no set scale, just whatever fitted into the box), but lengthwise they look OK with my existing ships.
The Convoy Escort is 7.9" long and the other two are 8.6" long. That makes the Escort between 200 and 230 feet at 1/300 and 1/350 scale, and the others 215 to 250 feet long. A Hunt class Destroyer is 262 feet long and a Flower Class Corvette is 205 feet, so they are a reasonable length.
The superstructure looks like a smaller scale, not 1/600 but a lot smaller than 1/300 or 1/350. I'm not sure whether to use then as they are, with some minor adaptation, or take all the superstructure off and scratch build new stuff.
I'm going to start with the actual WW2 model, the Escort Corvette.
Here's a comparison shot with a Warlord S-boat and a 3D printed Isle Trawler.
I'm going to start off by just giving it a new paint job and see what that looks like before I start any remodeling. Starting with a grey spray undercoat.
Hopefully I'll get a chance to add some more paint over the next couple of days.