Level is right I'm afraid - this is the basic mechanism, even if the logic is rather odd.
The ANO says that if the aircraft is not on public CofA, then only a single payment can be made. If the aircraft is jointly owned it's assumed that there's a payment into the syndicate; add in a payment is made to the instructor as well, that's two, and verboten.
In the meantime, this document seems to have vanished from the CAA / AIP websites, but here are some extracts I made a while ago for my own use:-
Extracts from CAA AIC: W 001/2011 27-JAN-2011 (FLYING TRAINING AND FLYING TESTS IN PRIVATE AIRCRAFT.)
2.2 Therefore, individuals are permitted to pay an instructor for training in their own private solely-owned or jointly-owned EASA aircraft....
3.2 ... a person who owns an aircraft outright and does not have to pay for anything else in relation to the flight is permitted to pay an instructor for training in their private aircraft. Likewise, a person who has free use of an aircraft is also permitted to pay an instructor for training in the aircraft, although this situation usually only arises when a close friend or member of the owner's family wishes to use the aircraft....
4.2 ...it is not possible to pay for instruction in a jointly owned non-EASA private aircraft; however, provisions have been made to allow some kinds of remunerated training in certain of these aircraft. The circumstances and conditions depend on the airworthiness regime that the aircraft is subject to and its intended use.
4.3 Operating under a CofA
4.3.1 A General Exemption (ORS4 No. 804)3 has been issued to allow owners of a jointly owned private aircraft operating under a CofA to pay for instruction in their aircraft with the following conditions and limitations:
a. The training cannot be for the purposes of becoming qualified for the grant of a licence or a rating in a licence (training and testing for revalidation or renewal is permitted).
b. For aircraft with a maximum take-off weight not exceeding 2730 kg, the last scheduled maintenance inspection must have been carried out by an appropriately licensed engineer or maintenance organisation and a Certificate of Release to Service issued.
c. There must have been no pilot maintenance since the last scheduled maintenance inspection.
d. The person undergoing the training must hold a pilot's licence that entitles them to act as pilot in command, or would entitle them except that they need to fly with an instructor/examiner to obtain a Certificate of Test, Experience or Revalidation and the
purpose of the flight is to gain such a certificate.
Note: Training for the initial issue of an NPPL, PPL, CPL, IMC Rating, Instrument Rating or other 'ab initio' training is not permitted. The intention is to allow individuals to pay for training that enables them to regain currency, renew a licence, learn a new skill (such as short field landings), become familiar with a new type etc.
ORS4 804 which is referred to in there has been superceded several times and is now ORS4 No.968
ORS4 No. 968: Flying Training / Checking | Publications | About the CAA
This *probably* shoots you down in flames I'm afraid [incidentally, the TB10
is an EASA aircraft for the purposes of the document. That said there's a reference at the bottom to:-
White AIC ‘Flying Training and Flying Tests in Private Aircraft’.
Which I suggest you try tracking down, as it sounds like there's a slim chance it might prove me wrong. Rather odd referring to an AIC by title only however, so that might be a small challenge.
G