Of course Heathrow is a hub for BA
On purely logical grounds, a hub for at least one airline counts as a hub, so I win
Double hubs - ie two airlines offering a genuinely expansive network of flights instead of just a few niche routes - are extremely rare. I think ORD & LAX would be the two obvious contenders in the USA, and.....
Triple hubs - even rarer. Yet for now at least - Bmi serve a mix of European routes + their north African & Asian routes. I think Virgin is certainly a hub operation, even if they may rely on others (esp BMI) to feed them.
I doubt you would say the same for Gatwick.
Although it must have a far higher ratio of point to point, are BA really interested in serving LGW-MAN, EDI & GLA just for the domestic traffic?
Some might use the term "focus city" perhaps?