British used 20mm Oerlikon and its simplified version, Polsten(I'm not sure if I remember the name absolutely correctly). For ex. Crusander AA tank was armed with a twin 20mm or a 40mm Bofors and haven't you see the old Airfix model on LVT Buffalo (+ a Jeep). It was armed with one 20mm Polsten and 2 .50s.
HTH
Juha
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