> but must accept legal tender in certain circumstances.
That's not what legal tender means in the UK and the misunderstanding causes some problems.
If I have a debt, and I attempt to pay in legal tender, and my creditor refuses to take it, I can say I've discharged the debt.
It has no use, in the UK, when I'm buying stuff in a shop.
http://edu.bankofengland.co.uk/knowledgebank/what-is-legal-t...
Nitpick:
Butcoin is not, to my knowledge, legal tender anywhere. What Indonesia has done is declare that all transactions in Indonesia must be denominated in rupiah. This is far more restrictive than most Weatern nations where private parties may accept anything they want as payment, but must accept legal tender in certain circumstances.