Straits Settlements 20 Cents In Copper

It could be very well be a mint error.

I have a standard bronze Mauritius 2 cents and a Ceylon 1 cent, which would have used very nearly the same planchet size. It is very possible that a planchet from one of these may have got mixed up with silver ones.

I have a number of off metal strikes of this type. It should be remembered that the British Royal Mint struck coinage for almost all of it's colonial possessions. Such a mix-up, although rare, did happen occasionally.

If that is the case, I think that this one may be quite rare, I have not seen one of this vintage.