I don't think you are going to be able to dot the "i"s and cross the "t"s on this one,
da42flyer. Certainly an aircraft vacating a runway or landing area is conventionally accorded priority over an aircraft taxying nearby, whether the law specifically says this or not.
You might like to look at the Rules of the Air (Section 2 of
CAP393), Rule 58 (Markings for paved runways and taxiways). Para (2) states that, with regard to the hold line prior to entering the runway area,
(2)... no part of a flying machine or vehicle shall project in the direction of the runway without permission from the air traffic control unit at the aerodrome during the notified hours of watch of that unit.
Para (3) also states:
(3) Outside the notified hours of watch of that unit or where there is no air traffic control unit at the aerodrome the markings referred to in paragraph (2) signify the position closest to the runway beyond which no part of a flying machine or vehicle shall project in the direction of the runway when the flying machine or vehicle is required by virtue of rule 42(3) to give way to aircraft which are taking off from or landing on that runway.
Both of these paragraphs could be said to further your suggestion that, until a landing aircraft has fully crossed and is clear of this line, the landing is not complete. In other words, it can be argued that the aircraft is, up to that point, "landing" rather than "taxying".
However, in the absence of a definition of "landing", I rather think this is the nearest you are going to get ...
JD
