Just make a cash dummy booking for a fully flexible ticket on BA.com (or if you have status, via your BAEC login, in which case it doesn't need to be flexible). After flight selection and before cash payment you should see the seat map. If you are doing a lot of flying then consider using ExpertFlyer.
Last edited by corporate-wage-slave; Dec 31, 2015 at 8:47 am
Reason: typo