In reply to Neil Williams:
Yep, you're quite right! From
http://www.britishairways.com/travel/bagcabin/public/en_us
You are allowed one piece of hand baggage plus a laptop or handbag.
A 23kg (51lbs) maximum bag weight applies and you must be able to lift the bag unaided into the overhead lockers in the aircraft cabin.
Please see below for sizes.
Your main piece of hand baggage is up to the dimensions 56cm x 45cm x 25cm (22in x 18in x 10in), including the handle, pockets and wheels.
Your bag must fit into the bag gauge, available at the check-in area.
Your laptop or handbag is up to the dimensions 45cm x 36cm x 20cm (18in x 14in x 8in), including the handle and pockets.
Your laptop or handbag must fit under the seat in front of you.