Agree with Paddy. These cupro nickel coins can look like silver. All of these tests are not conclusive. The cupro nickel and 50% silver half crowns (1920-1946) weigh almost the same. It doesn't look like silver to me which has a different patina. While it is possible, it was 4 years that silver planchet had to be hanging around before being struck in 1950.
If you do your test, it will drastically lower the value of whatever you have. Simpler to take it to a jeweler or college and have it weighed and then if it is something you will not have ruined the value.
You'd have to do a specific gravity test or XRF to confirm the composition. British coins don't change weight when the composition changes.