I've only just read this thread, how awful for you Gill. I'm so sorry that they are not getting on. I wonder what it is that's causing it - maybe since the first big scrap when they were onlead they are now alot more nervous of each other on the lead? I know my two really pick up on each other so much and it's more pronounced onlead.
My two rarely have a cross word but last week Zorro really went for Bella because she was moving around (actually trying to leave the room) and he had a scrap of hide chew - it's the first time they've had anything like a proper scrap, he just hurled himself at her (he's a year old but neutered) and that was bad enough (no blood, just two very upset dogs for a while).
I really hope you can get to the bottom of whatever it is - it must be so horrible for you at the moment.