If you want to question what can be done to stop this, then here's a suggestion. IT contractors have been plagued for about 10 years now by IR35. IR35 essentially states that if you are set up to run as a company or sole trader but you only supply your services to one client, then you are considered what HMRC terms "a deemed employee".
If you are in this category then you are liable for all the standard PAYE terms and conditions applicable...and hence your own limited company must pay you as such (drastically reducing your income - hence the IT contractors chagrin). Moreover, the - if I can term is such - "deemed employER" is ALSO liable for the company funded parts of this, such as NI contributions etc.
In the case of these latest offerings from Ezy and BRK - and freely stating that I do not know the terms of the deal and suspect that no company using this route would have been so dumb as to not check it out - it is absolutley clear that the "contractor" is a deemed employee.
If Balpa put their hand in the pants and find their nuts, they can pursue the legal point that these pilots are deemed employees. Succeeding in this would then put the employing airline in the position of having to pay backdated contributions to HMRC and quite probably a tasty little fine. I rather suspect that this would stop it dead.
Food for thought though...