There is no requirement to have the level of English included in a radio licence as these can be issued using different languages. The UK do not include either the level or an indication of English proficiency on the RT Licence.
ICAO now requires that a pilot licence be endorsed with the phrase English Proficient for all international flights. The UK do not enter the level on the licence, that information is held by the CAA.
It has been assumed that anyone who holds a UK RT Licence and has passed the related exams must be at least 4. Pilots are then required to renew this classification after 3 years or obtain a level 6 assessment at their next rating revalidation.