Thanks for all the suggestions so far. Yeah, I was being too optimistic about fitting in an island, thanks for confirming! In regard to the downstairs loo, it used to be in the teeny space on the bottom right of the kitchen plan, hidden under the stairs, and not up to the standard of any building regs. I'd still like to have one, which is why I've moved it on the plan to it's current location, but you're right it might be a bit smelly without the right ventilation. I can't really see anywhere else to fit one? Here's the floorplan (front door bottom right on to hallway with stairs, lounge bottom left):
I'm liking the idea @Bozza to extend out studs and gain extra worktop/storage space that way, with oven/fridge at the end (also gives some handy spots to hide pipes and wires). Great idea to put narrow units next to the chimney breast. @Sparrowhawk I think you've come up with the only way I could conceivably fit a penisular, but I think having to walk out round it to get to the dining table in the extension might irk me too much. @Temp rotatable island seems like an interesting idea, I might end up going for a breakfast bar mid-height table in that location which I can move about as and when.