A study by credit rating agency Standard & Poor’s has raised questions over the financial strength of some of the biggest banks ahead of new rules that could require them to raise more funds. The analysis by S&P showed that HSBC is the world’s best capitalised bank, while Switzerland’s UBS, Citigroup of the US and several of Japan’s biggest banks are among the weakest. The ranking of 45 of the world’s top banks highlights yet again the continuing capital shortfall at some key institutions.