I'll just add that the reason aircraft like that above received the Distinctive Markings prior to D-Day, when they most certainly weren't going anywhere near Normandy is two fold.
First, the markings were to be applied to all fighters (among other classes of aircraft), as specified in Operational Memorandum No.23.
Second, the markings were, explicitly, not just to identify aircraft as friendly to naval and ground forces, but also to other friendly aircraft. If fighters at OTUs and similar UK based units had not worn the markings they would have been exceptional and hence vulnerable to misidentification.
Cheers
Steve