But beware of this .... flew with Groundsow LHR/YVR in PE and I went to prebook seats together. Paid the fee then looked at the availability and there were no seats together apart from centre cabin. Unless they have changed it you can't see what is available until after you have paid the fee!
Decided to switch days so we could sit together, rang BA and they did this but then charged £65 for changing days. CRAZY SYSTEM. Told to write to Customer Relations and they would refund it.
Wrote as suggested and got a reply that they are sorry they have to charge a booking fee, clearly never read my e mail at all! Awaiting another reply now.... not with too much expectation of getting my £65 back!