Where's the violation?

Even if your hats theory is true (and I very much doubt it is, as applied in this situation), it would not do much for Red Hat’s case. The threat from Red Hat is not just to stop providing support services. If it were, a rebuild distro could just sign up for a single Red Hat license and redistribute the sources it receives; it has no need for support. Actually, the rebuilds *are* going to try that, but the assumption is that it will fail, because of course Red Hat is also threatening to cease further software distribution. Both the distribution that binds Red Hat to the GPL, and the threatened non-distribution that allegedly violates the GPL, are performed under the “distributor” hat.

As for the role of copyright owner, I imagine that anyone attempting to sue Red Hat over the affair would try to find a relevant copyright owner to act as plaintiff. However, you should note that the Software Freedom Conservancy, in its Vizio suit in the US, is currently testing the theory that recipients of GPL software have standing to sue over missing source code, as so-called third-party beneficiaries. If it succeeds, the same principle would presumably apply to Red Hat. I realize you are focused on UK law, but any suit against Red Hat would probably be in the US anyway…