i’d be very suprised if any bolts on a british aircraft were measured in millimetres (although i’m quite prepared to be proved wrong!).
american bolts have the diameter and length of the plain shank measured in 1/16ths of an inch, some english bolts have the diameter in 16ths of an inch, and the overall length (from under the head, to the end of the thread , including the thread), measured in 10ths of an inch.

they look like close tolerance bolts, with a ground shank , as opposed to a standard bolt. they could either have been used on an engine, or in a close tolerance part of the structure.
i’m not sure if they are TSR2 specific, as we still use similar (but not exactly the same) bolts today.