Great, thanks Dave. Not adding continents, just flights within the normal allowances. BA did try to whack me for the 10% last week but it was before my first intercontinental flight. They said if I waited until I had started they 'couldn't guarantee there won't still be a fare difference' which I interpreted as perhaps being a rule change I wasn't aware of. From what I've learned here it looks like being more an attempt to blag me 800 quid I didn't need to pay.

I'll call them again today and let you know if they contradict you.