For a boot to be long lasting, it has to be repairable, e.g. a Goodyear or storm welt or stitch down. Glued together shoes will never be BIFL because the soles are a wear item, particularly for hiking, because the rubber is often softer to better grip trails, but that trades off for less durability.

Anything with foam in it is a no-go because foam breaks down over time. For waterproofing, there’s a few different types. Rubberized boots are truly waterproof, and fairly durable, but they don’t breath at all, so you probably don’t want that for hiking. Performance waterproof boots will often have a gortex lining, so the leather can get wet, but that water doesn’t penetrate. That works really well, but the membranes break down over time, so they aren’t perfect. The last option is if the leather itself is waterproofed. This also makes it much less breathable, but it is more durable, and you can “repair” it by making sure to keep up with conditioners, etc.

I think if I were in your place, I’d look for leather boots with a storm welt, and then I’d wax all around the base and over the toe area. That will get those areas mostly waterproof, but you could leave the top of the upper unwaxed so it stays breathable. You’d have that area covered by your pants, or ideally gaiters, so water can’t get in.

I’m not sure about brands in the UK, though.