This week’s postcard shows a group of airmen from the Royal Air Force performing a display of physical training at a tournament:

The band can be seen in the background:

And the men themselves, dressed in white, performing their display of PT:

The arena itself is highly decorated, with blags, banners and streamers:

I suspect this is the Royal Tournament and the Daily Mail in 1935 reported on that years pageant:
This year’s Royal Tournament which the Prince of Wales will open on May 9 at Olympia, Kensington, will be more “Royal” than ever.
For the opening ceremony the Navy, Army and Air Force will provide a combined Guard of Honour 500 strong, and all the regiments and corps taking part in the subsequent programme will be those of which the King or his sons are titular heads…
Other features of the tournament will be massed physical-training displays including rope and ladder climbing by Army athletes, and the ever popular speed drills contributed by the Royal Air Force Training School at Uxbridge.
Boys from the Duke of York’s Royal Military School at Dover have devised a striking display which promises to be worthy of the famous toy soldiers’ drill which they first presented at Olympia some years ago.