So I'll need to undetake a "supervised" 150nm X country with two landings at airfields other than my home airfield. Should not be an issue.
What a quaint and ridiculous suggestion! As the holder of a pilot licence you are entitled to make such a flight within the privileges of your licence. There is no legal process by which a third party may interfere or supervise such a flight!
FCL.035 Crediting of flight time
(a) Crediting of flight time
(1) Unless otherwise specified in this Part, flight time to be credited for a licence, rating or certificate shall have been flown in the same category of aircraft for which the licence or rating is sought.
(2) Pilot-in command or under instruction.
(i) An applicant for a licence, rating or certificate shall be credited in full with all solo, dual instruction or PIC flight time towards the total flight time required for the licence, rating or certificate.
Therefore; so long as you can prove (log book) that you have met the requirement it qualifies under FCL-035. There is no validity period, so any flight that meets the requirement should suffice.
Most former Group A pilots did not complete a 150 nm X Country either, prior to 1 July 1999, the UK requirement was to have completed a flight which landed at two alternative aerodromes, one of which had to be 50 nm from the point of departure. Typically, this was around 130 nm and had to be completed within 9 months of the licence application. It could not be conducted until the Navigation Flight Test had been successfully completed consequently, this flight was usually conducted after all training and testing, had been completed and was referred to as the "Qualifier" for which CAP53 required a certificate of completion. This requirement ceased on 1 July 1999, the "Qualifier" was replaced by the 150 nm ICAO requirement, which now formed part of the training, and in any event was a precursor to the skill test. There has never been a JAA or EASA requirement for a separate certificate for this flight. The pre-JAA AOPA Certificate continued to be used for a number of years and was finally copied by the CAA who produced another unnecessary piece of paper. I can no longer find it on the CAA website, so they may have finally realised CAP53 died 14 years ago however; it is still referred to in SRG 1105.
Article 4 of Regulation 1178 includes an interesting statement:
7. A Member State may authorise a student pilot to exercise limited privileges without supervision before he/she meets all the requirements necessary for the issuance of an LAPL under the following conditions:
(a) the privileges shall be limited to its national territory or a part of it;
(b) the privileges shall be restricted to a limited geographical area and to single-engine piston aeroplanes with a maximum take-off mass not exceeding 2 000 kg, and shall not include the carriage of passengers;
(c) those authorisations shall be issued on the basis of an individual safety risk assessment carried out by an instructor following a concept safety risk assessment carried out by the Member State;
This of course keeps the French Brevet de Base alive after it was rejected from the original draft.