BOAC had in fact quoted the following:
9.1.1.1.2 An aircraft compelled to make a descent through MNPS airspace, whether continuing to destination or turning back, should, if its descent will conflict with an organized track:
a) plan to descend to a level below FL 280;
b) prior to passing FL 410, proceed to a point midway between a convenient pair of organized tracks prior to entering that track system from above;
c) while descending between FL 410 and FL 280, maintain a track that is midway between and parallel with the organized tracks; and
d) contact ATC as soon as practicable and request a revised ATC clearance.
...from a document Bigears had
linked to earlier:
"NAT Regional Supplementary Procedures (SUPPS) (Doc 7030) Working Copy – 5th Edition - 2008
This version of the Working Copy of the 5th Edition of the NAT Regional Supplementary Procedures (SUPPS) (Doc 7030), Amendment No. 3, dated 15 October 2010, includes the following approved amendment(s) which have not yet been published."
My point re. the above was that it was not relevant to the scenario outlined by the OP.
The document you refer to,
"GUIDANCE CONCERNING AIR NAVIGATION IN AND ABOVE THE NORTH ATLANTIC MNPS AIRSPACE Edition 2010", was last updated on 17th October 2011, (
link here), however, according to the ICAO webpage linked to above, the SUPPS were last updated on 4th July 2011. You be the judge.
For my part, allow me to misquote Kiefer Sutherland:
I have two books at my bedside, the MATS Part 2 and the King James Bible. The only proper authorities I am aware of are my Local Area Supervisor and the Lord our God.
The (SUPPS) non MNPS/RVSM descent through OTS does not make any appearance in our current MATS Pt 2; which is good until 2nd December 2011.