The boss of the Royal Bank of Scotland accused some of his own employees of not knowing right from wrong after RBS was fined almost £400 million in the latest scandal to hit the financial sector yesterday.

Taxpayer-owned RBS was one of five banks ordered to pay fines of more than £2 billion after traders attempted to rig the foreign exchange market.

HSBC, Citibank, JP Morgan Chase and UBS were also fined by the UK's Financial Conduct Authority (FCA) and US authorities. Investigators found staff from different banks used code names to work together to manipulate currency exchange rates.

Paper trails show the behaviour went on during the 2008 financial crisis, when RBS was bailed out by UK taxpayers to the tune of £46bn, and up until as late as 2013.

RBS Chief executive Ross McEwan added: "To say I am angry about the misconduct would be an understatement. We had people working at this bank who did not know the difference between right and wrong, or worse, didn't care about the distinction."

Transcripts of conversations released by the FCA showed traders referring to "free money".

The FCA warned the behaviour had undermined confidence in UK financial markets.

However, it added, there was no suggestion there had been any impact on consumers.

The Serious Fraud Office has launched a criminal investigation while RBS said it had placed six people in a disciplinary process.

FCA chief executive Martin Wheatley said: "The record fines mark the gravity of the failings we found and firms need to take responsibility for putting it right. They must make sure their traders do not game the system to boost profits."

The UK fines dwarf its previous sanction of £532 million for the Libor interbank lending scandal.

RBS, which is still 80 per cent owned by the taxpayer, was fined a total of £399 million including £217 million by the FCA and 290 million US dollars (£182 million) by the US Commodity Futures Trading Commission (CFTC).

The bank's chairman Sir Philip Hampton said: "The RBS board fully accepts the criticisms...and condemns the actions of those employees responsible for this misconduct."

Treasury minister Andrea Leadsom said the actions of ­traders were "completely disgusting".

"Every taxpayer will be completely horrified to see throughout that period of the financial crisis where taxpayers were bailing out the financial system, there was still a group of foreign exchange traders, and other traders, who decided they would rig the system to suit their bonuses - and that is absolutely disgusting".