Icao level proficiency runs up to a level six. If you are a native speaker then i think you are automatically awarded a level 4. Usually your verbal skills would be assesed on the renewal of a rating or licence and without a written test if once again you are a native speaker. Its a bit of a grey area in some JAA states as to the methods of testing, some are still trying to work out a method of testing!!, and varies from state to state, it is in fact supposed to be the same across all states but is still very fragmented. I would speak to the licencing dept with the CAA if your licence was issued in the UK but your not a native speaker. Im sure they would point you in the right direction as to where you can be assesed and how.