Your post does not make a lot of sense and it appears you have complete failed to understand the reasons of overbooking.
Having had access to BA booking systems for over 5 years, their Revenue Management system and department is impressive. They NEED to overbook depending on many variables like time of day, city pair, time of year, available seats in Business/ First, group bookings, and many many other factors. They almost always get it right. Without overbookings, planes would depart with on average 10% less passengers than actually booked. In the RARE event that more passengers who up, volunteers are asked to come forward for alternative travel route / time in exchange for compensation. Everyone wins, that is the message. Some flights will be overbooked by as much as 40-50 seats on long haul flights and still leave with empty seats.