Technically speaking, these assumptions aren't quite right, though it's easy to see where a wrong assumption applies. NMW *isn't* due to the self employed...but, as soon as an individual enters into contractual obligations, this changes. Actors are self employed (for tax purposes) but the union considers that they undertake jobs on the basis of contract. Equity hold that an actor is considered an employee of a company for the duration of their work contract (either written or verbal), and they are entitled to NMW, as any other employee would be. That many don't lay claim to the NMW and, so in a sense, 'waive' their right to it, is a different issue.
There was traditionally a 'grey area' surrounding whether Equity's claims could be upheld in a court of law - although the union always held that the following stipulations are enough to prove that an individual is not being taken on as a 'volunteer':
1. The individual is engaged to work set, specific patterns of hours (i.e. the actor is given a rehearsal schedule, and, even more importantly, a production schedule, which they have to adhere to)
2. The individual has been promised 'payment in kind' in return for their services (i.e. they have taken the job on *on condition* that, in lieu of pay, they will receive a copy of their own work)
3. The individual has been promised a 'reward' for engagement on the project (i.e. they have been promised that, if they undertake this unpaid trailer now, it will lead to their being cast in paying work in the future) etc.
What has been happening in recent months is that court rulings have definitively been showing that judges are siding with Equity's viewpoint, and supporting the actors' right to be owed NMW, on 'profit share' and student film productions.
Some companies have been moving towards paying NMW in consequence: it does not amount to a vast amount of money, and there may be false assumptions about how much is actually generated by NMW payments, but, for e.g. an 8 hour day of filming, it works out at about £60 a day.
Many companies continue to avoid paying NMW: there *are* loopholes here, some of which Equity supports in order that innovation can continue to flourish on the Fringe and that e.g. graduate companies are not hounded out of existence. The union maintains that an honest collaboration in which all financing and profits are shared equally does not, in law, constitute the creation of employer/employee status, and so is not subject to NMW.
Equity tends, of necessity, to end up fighting rearguard actions - which is to say that it's harder to force companies to comply with paying NMW in the first place than it is to encourage legal action to be taken against them afterwards. And, in fairness, the union have never been overly keen to establish the payment of NMW as some kind of benchmark replacement for payment at higher, union negotiated rates, for obvious reasons. But it shouldn't be thought that actors have no right to claim for NMW, as they do.
