ACPO's weasel response to the Mail - "The president of ACPO wears the uniform of a Chief Constable because they hold that rank in law" - does not accurately reflect the requirements of s.96 of the Police Reform Act 2002:-
If a person who holds the office of constable becomes the president of the Association of Chief Police Officers of England, Wales and Northern Ireland, he shall, while he is the president of that Association—In other words, Orde remains a constable in the PSNI with the rank of Chief Constable and is subject to that force's uniform regulations.
(a) Continue to hold the office of constable; and
(b) hold that office with the rank of Chief Constable (my underlining)
It may seem a minor point, but consider that if the man can't resist this fantasy dressing-up when just a candidate for Met Commissioner, what Ruritanian uniform embellishments will he be unable to resist if appointed? London could be the laughing-stock of the world with a Commissioner dressed like Idi Amin ...