بسم الله الرحمن الرحيم
Any eatable or drinkable thing cannot be termed haram until it is not confirmed or known that its ingredient contains any haram and impure thing. We do not have any knowledge about Cadbury chocolate. The same is the rule of the chocolates of other companies.
الأصل في الأشياء الإباحة (قواعد الفقه)
Allah knows Best!
Darul Uloom Deoband