Once the doors are closed and steps etc removed the easiest way to remove forgotten items from the aircraft is via the flight deck window, suitably wrapped and weighted. I have done it many times on the ramp and occasionally on the taxyway, but always to a member of staff and with the help of ATC.
The question is why were ATC so unhelpful, even obstructive and why the heavy handed approach with police involved.
With the information available I would have thought that apologies from Airport/ATC to airline, crew and passengers were necessary.
Seems to have been a jobsworth approach by airport staff and I hope the airline remonstrates with the airport.
One can only speculate that had the airline been say Ryanair then Michael O'Leary would probably withdraw from the airport tomorrow.
I hope BA shows some backbone and supports its crew.