Indeed - my own area of work is alongside some of these people. People's status can indeed change from job to job, depending on the skills needed. The registered door keepers, with the security checks and badging (and importantly) direct criminal responsibility if they act poorly. If, as does happen, doormen get arrested after an incident, they are on their own - no employer, no manager, just a booking agency. People like Showsec use self-employed people for the key jobs, and people taken on as PAYE, because they recognise the distinction, and as far as I'm aware, so do HMRC. In the entertainment and music industry we can have very strange classifications for work. It's common for a working team of people to be individual contractors - self-employed people, invoicing for their work alongside others who are paid their contract fee divided by the length of the production, weekly with no tax or NI deductions, while others simply because the contract contains the word 'performer' fall under one of the negotiated HMRC exceptions and get their contract fee less Class 1 NI, but no tax! These people can end up paying Class1, Class 2 and Class 4 NI - which is very strange, but correct.
I've got one contract coming up where I change status during the working period. I get a simple fee on production of a VAT invoice for part 1, then when hats change, the invoice for the next period will NOT be paid in full, as NI will be deducted! Make that work in your accounts! Balancing payments grrrrr.
Back to the security people. Back in 2005, the security guys were invoicing clients direct, but the hassle was not taxation, it was coordination. The current agency style system is much better, and the clients don't need to know who is coming, just the quantity. The individuals invoice the agency for days worked. If they arrange cover themselves, it's perfectly fine - IR35 seems very straightforward. No doubt HMRC could well interfere.
I'm not sure that losing money is something they concern themselves with, just meeting the rules, the guidelines and the trends and rule interpretation. If a sector as a 'whole' appear to be avoiding instead of minimising their tax liability, then they'll alter the system - they rarely seem to target individuals on these cases, because of the rubric it creates.