Made by Herbert Johnson, Hatters to the Late King George VI.
King's crown gilt cap badge & KC chin stay buttons. 
Not sized, this is on the large side for me and I measure a size 56 cm, I'd suggest it would fit a size 57-58 cm.
Comes with the original box which is named to Major J.M.G. Bausland R.A.
 
Condition: a few small barely visible moth nips / traces mainly to the red band, under the overhang.
Weight: 328 g on own and  1.64 kg in the box.