Banks must set aside enough capital to cover losses on any bitcoin holdings in full, global regulators proposed on Thursday, in a "conservative" step that could prevent widescale use of the cryptocurrency by big lenders. The Basel Committee on Banking Supervision, made up of regulators from the world's leading financial centres, proposed a twin approach to capital requirements for cryptoassets held by banks in its first bespoke rule for the nascent sector. El Salvador has become the world's first country to adopt bitcoin as legal tender even though central banks globally have repeatedly warned that investors in the cryptocurrency must be ready to lose all their money.