Based on the image you have shared, the coin appears to be a British 1 penny coin rather than a Sri Lankan coin. The coin was minted in 1940 and features the image of King George VI on the obverse side. The reverse side of the coin features a seated Britannia with a shield and trident.
During the time period you mentioned, Ceylon (now Sri Lanka) was a British colony and used British currency. It is possible that this coin was used in Ceylon during that time.
In terms of value, the worth of a coin depends on factors such as its condition, rarity, and historical significance. Based on the image, I am unable to assess the coin's condition, so I cannot provide an accurate valuation. If you would like to get an accurate valuation, it is best to consult a professional coin dealer or appraiser.