The Oerlikon Type S gun (which used the 20x110RB case) was not fitted to any British aircraft. Its main aircraft operational use was in some French fighters, although it was being replaced by the Hispano at the start of the war. The Hispano cartridge has very similar measurements (20x110) but the shoulder is less sloping and the rim is not rebated (in the Oerlikon case, the rim has a smaller diameter than the body). You can see these rounds illustrated in the pic from the Ammo Photo Gallery on my website. Be warned, though, a fired Oerlikon case had the neck 'blown out' - so it is better to look at the rim.
Tony Williams: Military gun and ammunition website and discussion forum
