WARNING: BA online
You may not fall for this, but I think I am not the only one who has. When booking online and choosing by lowest fare selection you will get lots of traps laid out for you. In my case I booked two separate domestic-longhaul return flights and only twigged that although I had selected a Heathrow link out they had sneaked a Heathrow-Gatwick transfer in on the return - both times. Yes, you are supposed to check carefully, but when you are somewhere abroad that only has slow dial-up which keeps timing-out, urgency becomes quite important if you are going to succeed in completing the booking. Afterwards I discovered that Heathrow was excluded from the list of choices by �2.60 - the transfer costs �17.50, quite apart from the time and general inconvenience. The odd thing is that even when you choose to carry out a one-way search from Heathrow they will still give you a Gatwick choice as the cheapest (I hope you know LGW is Gatwick, Heathrow is LHR if not you could be fooled). You would think that BA could be more friendly and employ more common sense in their software. What I have sort of been forced to do is to buy a separate one-way ticket from Heathrow to ensure I can get the baggage checked through to the domestic destination. Nice scam, eh ?