FT.com – Switzerland’s UBS (NYSE:UBS) has always been one of the world’s best capitalised banks. The purpose of holding extra capital, above the regulatory minimum, is to reassure clients that UBS can absorb any losses it might suffer in a downturn. Yet no sooner has UBS hit trouble – a $10bn write-off linked to US subprime mortgages, on top of $4.7bn a few months earlier – than it has joined Citigroup (NYSE:C) in raising more capital.