Here's a thought. There is another photo of the same soldier, very obviously wearing a Polish uniform but with the same white shoulder boards here:
Stanislaw Szklarski and colleagues | Hall of Memory
His service record also says he was a waiter in 5 Division HQ... I'm assuming the Officers'Mess.
Stanislaw Szklarski MOD file 13c | Hall of Memory
Is it possible that this was some catering token to kitchen whites... they had to wear uniform but had the white shoulders as a sort of waiter's uniform? Just thinking out loud!