Article 8 of the Aircrew Regulation:
(2) Applicants for Part–FCL licences already holding at least an equivalent licence, rating or certificate issued in accordance with Annex 1 to the Chicago Convention by a third country shall comply with all the requirements of Annex I to this Regulation, except that the requirements of course duration, number of lessons and specific training hours may be reduced.
There is an excerpt with some explanatory notes in CAP 804, Section 4, Part Q, Subpart 2, page 1.
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