http://www.britishairways.com/en-gb/...age-allowances

This is the link the BA's checked-baggage-allowances whatever mode of booking.
Its 3x32kg in business class for long-haul.

This is further down on the same page. It applies when both outbound and return journey are on the same ticket
If your journey includes flights in more than one class, the more generous allowance will apply to your whole journey

BA agents do not always make correct statements. That is why this forum exists.