Yes.
Following wording from CAA eu exit microsite:
EASA Part-FCL/BFCL/SFCL Examiners who hold an examiner certificate issued by an EASA member state will be able to continue to undertake Skill Tests, Proficiency Checks and/or Assessments of Competence, for the period of its validity up to a maximum of two years.
Alongside that they should probably also hold the following validation letter which validates their licence for uk purposes.
https://publicapps.caa.co.uk/modalap...etail&id=10006