See
CAP 804 Section 6, Part A, page 3 for credits:
The holder of a valid CPL or ATPL Licence issued in accordance with ICAO Annex 1 by another ICAO contracting state (including any JAR-FCL/Part-FCL pilots’ licence) who also holds a valid radiotelephony licence issued in accordance with Article 37 of the ITU Radio Regulations and has in excess of 1500 hours flight time engaged on international public transport flights, will be credited with the practical RTF Communications test and PPL Communications theoretical written examination; provided that the licence is valid and the practical test was conducted using the English language and English Language Proficiency is shown on the licence.
Assuming you meet the above criteria, you will still need a English Language Proficiency assessment by a UK examiner. If you're Level 6, any holder of a UK examiner certificate or FRTOL examiner will do. They can conduct a face-to-face assessment in accordance with
CAA Standards Document 51.
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