in brief, regarding Display Authorization regulations, for the UK, CAA CAP 403, Part A - Pilot Display Competency, only stipulates that evaluators (the equivalent of a TRE) should "normally be an active Display Pilot."
Flying Displays and Special Events | Air Operations | Operations and Safety
EDIT: and..."In addition to a valid Certificate of Test and Competence, a Display
Pilot is required to meet certain recency requirements before his DA is
valid. In the 90 days preceding a demonstration at a flying display for
which an Article 162 Permission is required, a minimum of three full
display sequences must have been flown or practised, with at
least one display sequence flown or practised in the specific type
of aircraft to be displayed."
and "If the display sequence has not been practised recently, the pilot
should set himself appropriately higher minima, for practice or actual
display purposes, until such time as full currency is regained."