One thing I've learnt since I've been on this board is that if a member of BA staff asks something, they're usually right and it's best to comply. The fact that you were allowed in 1E at landing is may point to the fact that you could have been allowed there for take off too but all in all it sounds like a minor inconvenience. Imagine on a full flight if they had the tables in the middle, they might have offloaded you!