Britain's Chancellor of the Exchequer, Alistair Darling, attends a news conference at the G20 Finance Ministers meeting, in central London September 5, 2009. ISTANBUL, Oct 3 (Reuters) – The Group of 20 major nations may blacklist countries that have lax financial regulation and impose sanctions on them, mirroring its crackdown on tax havens, Britain’s finance minister was quoted as saying.