From the CAA:
CAP1369 Camera Mounts Guide
Reference: CAP1369
Title: Camera Mounts Guide
Description: If you wish to attach a small camera (such as a GoPro) to a non EASA certified GA aircraft then the attachment needs to be inspected by a Part66 licensed aircraft engineer or via the CAA as a minor modification to the aircraft. To approve any installation the engineer will need to complete a maintenance release checklist and complete the aircraft logbook entry. For aircraft overseen by the British Microlight Aircraft Association or Light Aircraft Association those organisation’s requirements apply.
Status: Current
Review Comment: None
Version: 1
Date: 27 January 2016
Worth noting
This policy is applicable to non-EASA GA aircraft that are subject to UK CAA regulatory oversight, (CAP 747- Mandatory requirements for airworthiness contains the list of specific EASA and non-EASA aircraft types
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it is intended that CAA will provide a copy of this CAA policy document to EASA for potential inclusion in a future update to CS-STAN so that the camera mount policy can be extended to EASA aircraft