"Hit the ratchet handle with a hammer might do the trick."

Never hit a ratchet! Although we all do it, a ratcht should never be used to try and break/undo a bolt/nut from it's tightened position. All of the force is taken by the small ratchet gears inside the head and they aren't designed for that. If it doesn't undo straight away, use a bar.
Blaster/Kroil a good idea (neither available in the UK) and Loctite softens with heat so even a mini-butane torch should work on small jobs like this.