Very grey area
I do know of a case of phone bugging within the NHS, a doctor had his hospital internal phone bugged by the managment. It would seem that this is not illegal as long as it Is only the internal phone.
What followed was legal action by the BMA on patient confidentially issues, it never got as far as court but the NHS manager was fired and the doctor was paid a great deal of money to take early retirement.
My guess is BA found themselfs in the same grey area and decided not to take the risk of getting this into the public eye with a court case that they might not win ( despite not having the to contend with the doctors rock solid confidentiality issues)