Thanks everyone, so I screwed up a bit. I only booked the long haul as it was a 2-4-1 & I snapped up the CW seats online, and as I couldn't include a OW partner on 2-4-1 I assumed it had to be a separate booking. I guess I should have done them at the same time by 'phone. Not sure if BA would really abandon us if a OW partner is cancelled ( we have 10 hours float for a delay), but I suppose by next Feb a LTG (twice) will be scum. I'll stew on the risk vs cancelling at £70 to make a new 'phone booking.
Thanks again folks.