New rules that require banks to do more to protect themselves against trading losses will force them to increase their total capital holdings by an average of 11.5 per cent, according to an impact study by the Basel committee on banking supervision.

The rules, adopted in July by the committee’s 27 member nations, force banks to set aside capital against the possibility of credit defaults or downgrades and to test their trading-book risk in deeply stressed markets. All major banks must adhere to the new requirements by the end of 2010, including those in the US, which has not subscribed to some of Basel’s rules in the past.