Ryanair
Head of the CAA says they cannot withdraw routes from Ryanair, as they are registered in ROI, not UK. Surely, however, some punitive action is possible - suspend overflight or take-off/landing rights: 6 weeks of "restricting" their activities would go a long way to solving Ryanair's piloting situation - and UK customers would KNOW that their flight was cancelled.
BTW, Ryanair have the cheek to advertise on TV- I saw an advert on Thursday evening - although I could hardly believe it !