[stephen low]

Concur with the Falcon comment above as I had a BF XR8 that moved both brake and accelerator fore / aft which helped with my stumpy legs.

So must be permissible under the ADR's though this is a different piece of engineering to what is pictured but the concept is the same.

I'd have thought that if it can be safely locked to not move during driving, and maintains control functionality, why would it not be allowed.

Again agree, ask your engineer for definitive advice.