That is the first time I have ever, on PPRuNe or elsewhere, heard anyone describe the law in this area as "pretty simple really."
Simple?
It is nothing short of a disgrace that the ANO is so appallingly written and so difficult to understand. The CAA expects pilots and operators to comply with provisions, and may prosecute them if they fail to do so, yet even lawyers who specialise in aviation don't find the provisions easy to understand.
Here's an example of what the CAA regards as acceptable legislation for modern times. You can't get much more 'modern times' than this - it came into force about a month ago on 20th August.
Article 157. Public transport and aerial work—general rules
(1) Subject to the provisions of this article and articles 158 to 163, aerial work means any purpose (other than public transport) for which an aircraft is flown if valuable consideration is given or promised in respect of the flight or the purpose of the flight.
(2) If the only such valuable consideration consists of remuneration for the services of the pilot the flight shall be deemed to be a private flight for the purposes of Part 3 of this Order.
(3) Subject to the provisions of this article and articles 158 to 163, an aircraft in flight shall for the purposes of this Order be deemed to fly for the purpose of public transport—
(a) if valuable consideration is given or promised for the carriage of passengers or cargo in the aircraft on that flight;
(b) if any passengers or cargo are carried gratuitously in the aircraft on that flight by an air transport undertaking, not being persons in the employment of the undertaking (including, in the case of a body corporate, its directors and, in the case of the CAA, the members of the CAA), persons with the authority of the CAA either making any inspection or witnessing any training, practice or test for the purposes of this Order, or cargo intended to be used by any such passengers as aforesaid, or by the undertaking; or
(c) for the purposes of Part 3 of this Order (other than articles 19(2) and 20(2)), if valuable consideration is given or promised for the primary purpose of conferring on a particular person the right to fly the aircraft on that flight (not being a single-seat aircraft of which the maximum total weight authorised does not exceed 910 kg) otherwise than under a hire-purchase or conditional sale agreement.
(4) Notwithstanding that an aircraft may be flying for the purpose of public transport by reason of paragraph (3)(c), it shall not be deemed to be flying for the purpose of the public transport of passengers unless valuable consideration is given or promised for the carriage of those passengers.
(5) A glider shall not be deemed to fly for the purpose of public transport for the purposes of Part 3 of this Order by virtue of paragraph (3)(c) if the valuable consideration given or promised for the primary purpose of conferring on a particular person the right to fly the glider on that flight is given or promised by a member of a flying club and the glider is owned or operated by that flying club.
(6) Notwithstanding the giving or promising of valuable consideration specified in paragraph (3)(c) in respect of the flight or the purpose of the flight it shall—
(a) subject to sub-paragraph (b), for all purposes other than Part 3 of this Order; and
(b) for the purposes of articles 19(2) and 20(2);
be deemed to be a private flight.
(7) Where under a transaction effected by or on behalf of a member of an association of persons on the one hand and the association of persons or any member thereof on the other hand, a person is carried in, or is given the right to fly, an aircraft in such circumstances that valuable consideration would be given or promised if the transaction were effected otherwise than aforesaid, valuable consideration shall, for the purposes of this Order, be deemed to have been given or promised, notwithstanding any rule of law as to such transactions.
(8) For the purposes of—
(a) paragraph (3)(a), there shall be disregarded any valuable consideration given or promised in respect of a flight or the purpose of a flight by one company to another company which is—
(i) its holding company;
(ii) its subsidiary; or
(iii) another subsidiary of the same holding company;
(b) this article "holding company" and "subsidiary" have the meanings respectively specified in Section 736 of the Companies Act 1985.
Those are just the "general rules." You then have to turn to the exceptions set out (in similar 'easy to understand' style) in Articles 158-163 inclusive.
Pretty simple really.
Even the guidance (CAP 393 Air Navigation Order and Regulations)
written by the CAA, and intended to assist people to understand the virtually incomprehensible relevant provisions
written by the CAA into the ANO, contains a disclaimer!
Some examples from PinkPilot's understanding of these "simple" rules:
"Is somebody making money from the flight?" That's not the test.
"aerial work can be either a public or a private flight."
'Aerial work' is a category of Private flight.
"So....how do you figure out if it's a public transport flight. Simple - are there any paying passengers on the flight where a passenger is defined in the ANO." That's not the test.
"Aerial Work - but in the public flight category"
"Is somebody making money from the flight - yes they are so it is Aerial Work" The CAA might well say that, but the ANO doesn't.