Dinky Toys 351 Interceptor plastic missile yellow with black tip.
Also available in White with Red or Black Tip and Yellow with Red Tip.
If the missile appears loose when you fit it and it sits out or hangs down at the front then you can trim a bit off the rear of the missile. They are made a bit longer for worn mechanisms. Just trim 1 or 2 mm at a time (not inches!!) with a sharp blade knife, testing after each trim to get a better fit.