PricewaterhouseCoopers LLP, one of the "Big Four" accounting firms, is being investigated by a U.K. regulator over a possible accounting scheme in the firm's auditing of investment bank Barclays Capital Securities Ltd.

The Accountancy and Actuarial Discipline Board is looking into PwC's role in reporting to Britain's banking regulator Financial Services Authority in respect to Barclays Capital's compliance with the FSA's client-asset separation rules between 2001 and 2009, the London-based accounting watchdog said in a statement Friday.

In January, the FSA fined Barclays Capital £1.1 million ($1.7 million) for putting client money at risk over an eight year period. From 2001 to 2009, Barclays Capital failed to segregate client money maturing from its sterling money market deposits on an intraday basis. The money was segregated overnight but matured into a proprietary bank account and were mixed on a daily basis with the investment bank's own funds, typically for between five and seven hours within each trading day, regulator said at the time.

Under the FSA's client money rules, firms are required to keep client money separate from their own by holding it in segregated accounts with trust status on an intraday basis. This helps to safeguard and ring-fence the client money in the event of the bank's insolvency.