I'm not convinced market forces have much to do with Derek Thompson's pay. I really doubt many viewers are tuning in to Casulty just to watch him. I also doubt there's a big queue of producers wanting to poach him for the latest Netflix blockbuster or ITV's new drama.
I don't have an issue with big salaries for big jobs. I think that's entirely appropriate and some of these salaries aren't that massive relative to the industry or the UK in general.
What is obscene are the disaparities. Disparities anyone senior at the BBC could have checked and rectified before now but they chose not to do that.
I would axe some of the overpaid dead wood (Ian Beale, Charlie from Casulty, Nick Knowles) or at least offer much, much less at contract renewal and pay a fair rate for the job, not the personality (exception being where the personality IS the job). The BBC does a great job or training and developing talent so there's not going to be a shortage of people to fill jobs.