This was asked of me, so I put together a quick explainer. A bit rushed, but if I've misunderstood what you wanted to know or if it's unclear, tell me and I'll have another go. Also, not meaning to patronise you. One or two things are aimed at also helping readers who may not understand the issue in the way I know you do.
If only certain provisions in an agreement are void under the Competition Act 1998 and they are capable of being severed from the rest of the agreement, then the remainder of the agreement may be enforceable. The ordinary rules of severance apply. The doctrine of severance in contract law basically allows an illegal or uncertain contractual provision or even part of one to be removed from a contract, while the validity of the remaining provisions is preserved.
The Supreme Court considered the issue in 2019 in the case of Egon Zehnder Ltd v Tillman. In doing so, the Court overruled existing case law and developed a new test for severance of offending contractual provisions to be permitted, and it applies to provisions in agreements (and the PL's rules have contractual force) as follows: first, the words that will be severed must be capable of being removed without the need to add to or modify the remainder; and second, the removal of those words should not generate any major change in the overall effect of the agreement.
Of course, what constitutes a “major change” is rather subjective and there's scope for considerable argument. It wasn't inevitable that City would win on that point in APT 1, but I thought that the arguments insofar as it was possible for us to tell from outside looked pretty good for us and the club evidently did win. If City prevail in APT 2, meanwhile, then severance would operate so that there'd be a fucking great big hole where the shareholder loans provisions should be. Usual disclaimers apply, bard for me to see how that wouldn't be a "major change", TBH.