I imagine they'd be more likely to rely on Article 20:
"(3) In any particular case the CAA may direct that an aircraft registered in the United
Kingdom shall carry such additional or special radio communication or radio navigation
equipment as it may specify for the purpose of facilitating the navigation of the
aircraft, the carrying out ..............."
since the CAA does specify in the AIP the carriage of B-RNAV equipment in certain controlled airspace above FL095.