There were no British Half-Sovereign coins minted from 1938 to 1979 inclusive
Without knowing what the particular stamp is and it's condition, it is impossible to value. There was more than one stamp issued during WW2.
The tulip stamp was marked as the F Flower stamp. It has a face value of 29 cents.
The rioting an boycotting were harming British trade.
It is a forever stamp. It is good for the current value of a first class stamp.
Between $100 and $400, depending on the exact model and most importantly, the condition.
50-275 USD or so
Stamp act
The British Government passed the Stamp Act to help pay for British troops stationed in the Colonies
The value of a Top Value Stamp, "Toppie," the elephant sign is approximately $42. The better the condition of the stamp, the more money it will be worth.
Face value of the original stamp was $0.20
The value of the 1910 1955 penny stamp value is one pound.