The problem is that at BA you can be off sick without anyone checking up. All you have to do on returning is fill in a form to say you were off sick. No details about why.
There are checks which are triggered at a certain level and staff have become wise to these levels, keeping sick leave to a level just below the trigger point.
It's a hard one to solve, because any solution will need resourcing to run it (e.g. people with the right skills, not someone without a role drafted in) and it'll have to be done in a way that it helps those with real health problems while catching the abusers.
Mark.