Gate staff need to be hawk-eyed when boarding passengers by seat row numbers. Also, this will not solve the 'too much cabin baggage' issue.

The first few passengers who board (I'd say about the first third of the passengers) have used up almost all of the overhead locker space. The remaining 2/3 of passengers then have to spend a LOT of time fiddling around and rearranging bags already in the overhead lockers to get their bags in.

On my return flight last week I observed several passengers who were seated towards the rear of the aircraft but decided to use overhead locker space towards the front of the aircraft. Those seats were empty at the time. When those passengers who were seated towards the front of the aircraft boarded, they had to trundle down to the rear of the aircraft to stow their bags and then come back up the aisle to be seated.

BA is not addressing the root cause of the boarding time delays: too much carry-on baggage. Until that is addressed, no experiments in queuing theory will have any positive effect, in my opinion.