Apologies for taking this a bit OT but I'd like to know if there's a practical and reasonably humane* way to stop cats ruining soft furnishings.

Use a slip cover?

I dunno... I have two cats, both clawed, and neither of them hurt the furniture, even though it's shabby furniture. They do have a scratching post that they maul, though. When I brought home the scratching post, I carried each cat over to it, took it's front paws in hand, and made scratching motions. They caught on pretty quick. I don't think I've ever had to get after them for scratching the furniture.

Oh, the other thing I do that helps, is to trim their claws every few weeks.