Scandal-hit Barclays bank says it's facing yet another investigation - this one relating to the billions it raised from Middle Eastern investors back in 2008.

The bank said that Britain's Serious Fraud Office was looking into whether Barclays was open enough about what it had paid advisers when it raised more than £5 billion (NZ$9.8b) of emergency capital at the height of the global financial crisis.

The private lifeline helped Barclays avoid the humiliating government bailouts that the Royal Bank of Scotland and Lloyds were forced to accept after high-flying executives overloaded the banks with unsustainable amounts of debt.

Barclays' corporate reputation is already under siege after scandals over selling small businesses complex financial products they didn't need and revelations that the bank fixed a key market interest rate.

- AP