If it is about a size of a quarter it must be a sovereign (it's a little smaller than a quarter though). Half sovereign is about the size of a cent.
Ask your friend to check for a mint mark above the date. If he is lucky the coin could be minted in freshly opened mint in Ottawa, mint mark "C". In this case the coin would cost more than just the bullion value. If the mint mark is M, P, or S (all Australian), or none at all (Britain) then it's nothing special.