Britain and France don't import oil from Iran. The gesture was symbolic. Iran has offered their client countries long term oil contracts. If they refuse to agree to Iran's conditions, then Iran will refuse to renew existing contracts.
Most likely, countries that really don't care about the US and Israel's dispute with Iran will stop buying Iranian oil with $US. Given the way the US is running up a debt, getting off the $US before it collapses might be a smart move. Certainly this is an opportunity for large stable economies to challenge the $US as the international currency. Iran's biggest clients are China, India and Japan While Japan is following the US's lead, they can't reduce their Iranian oil imports to 0. they seek an exemption. China and India could offer to buy Iranian oil with their own currencies.