Thanks for that! A few other things I've noticed which may help pin down whether it is wartime or post war. There is a ticket pocket under the belt, and double hook and eye fastening between the third and forth button. The belt (with a staybright buckle) has the name "Perrens" on it, which matches the name in the tunic; the stitching on the edge of the flap that holds the buckle in place looks to me to be a self done jobby, and not tailored, which would fit in with the buttons and belt buckle being replaced. The tailors label on the inside reads:
HJ Nicoll & Co Ltd
London & Paris
No 3812 Cutter 9
P/O D F Perrens
As mentioned earlier, the rank was that of a Wing Commander, however the centre row of lace was in better condition than the outer two, on both sleeves (which suggests to me the officer in question cheated and just removed the half stripe and replace it with a full stripe when he got promoted; the stripes looked a bit too close together to me as well), and the lining had been torn in the sleeves, which confirms to me he promoted it himself, as the rows of lace had been sewn into the seam.
Amazing what you can requesition from school costume departments!