I think that whichever company that you use, they have an obligation to notify HMRC if something isn't right. I believe TCB made it a criminal offence if they don't several years ago.
Chatting to some friends , I understand that some of our Ryanair friends have been nabbed in the past as they were sailing very close to the wind with respect to non residence status, 180days in the country and no other fixed address. It doesn't pay to mess with HMRC.