I’m struggling to find anything online relating to Rule X and I’m slightly confused by the presence of references to Rule X.3.2 and Rule X.5.2 in the tweet, but the way I read parts 3, 4 and 5 of that tweet is that within the PL rules the only way City could successfully challenge the PL’s assessment that the Etihad deal was outside FMV via the arbitration process, was to prove (on the balance of probabilities) that particular decision by the PL was so unreasonable, that no properly minded [PL] board would have arrived at the same conclusion.
This is an extremely challenging burden to discharge. If the arbitration panel felt the decision was harsh, wrong, or even unreasonable then this alone would not be enough, and that part of City’s claim would fail.
And because the PL’s key live witness in respect of that aspect of the case, Mai Fyfield, gave credible evidence (and presumably came across as reasonable) this became an impossible burden for City to discharge.
The test referred to is essentially the same as the public law cause of action where (in very broad terms) to successfully challenge the decision of a public authority per se (where it has been made within that authority’s lawful powers) that decision has to be held by the High Court to be ‘Wednesbury Unreasonable’ following a case about a cinema in that Black Country town from the 1940s, (which I have actually stood outside when I’ve been in the town as it’s still standing, and is now a disused bingo hall!)
en.wikipedia.org
There are three broad gateways to a decision by a public authority being Wednesbury Unreasonable, one being the following: a decision that was so unreasonable that no reasonable authority could have possibly made it.
It’s a notoriously difficult burden to discharge and essentially requires the claimant to demonstrate irrationality in making the decision on behalf of the defendant public authority.
This test is very similar, if not practically identical, to Rule X.3.2/Rule X.5.2.
That’s how I read it anyway!