I'm sure someone at LHR has got wind of the fact that crews are by-passing the system: they are claiming their bag is going in the hold on the Manifest whilst actually putting it in the cabin (with an oversize bottle of shampoo etc).
If this is true (and it well might be), the LHR crews have only themselves to blame...IE: the few that are 'clever' have spoiled it for the rest.
Quite typical.
