Dozens of staff at Royal Bank of Scotland are expected to learn early next year whether they will be disciplined over the foreign exchange market-rigging scandal that saw it fined £399 million by regulators.

RBS, 80% owned by the taxpayer, has said it is reviewing the conduct of more than 50 current and former traders who were involved in the part of the bank that was the focus of a probe by US and UK officials.

It has also been looking into the conduct of dozens of individuals as part of a review of supervisors and senior managers responsible for the foreign exchange business at the time.

So far, six employees have been placed in a disciplinary process, with three currently suspended, pending investigations.

The bank expects to complete the review in the first quarter. Full-year results are due on February 27 but there was no indication on whether the outcome of the investigation would be ready in time for that announcement.

Meanwhile, RBS said 18 individuals had had their bonuses suspended. These will not vest until the process is complete. The review is being led by the Jon Pain, the bank’s head of conduct and regulatory affairs.

Mr Pain said: “We are undertaking a robust and thorough review into the actions of the traders that caused this wrongdoing and the management that oversaw it.

“This is a complicated process but also an essential one in order to identify culpability and accountability for this unacceptable misconduct.”

He said no further bonus payments would be made or unvested bonus awards released to those under the scope of the review until the review had been completed and its recommendations considered by the remuneration and board risk committees.

Mr Pain added: “There is no place for any misconduct at the RBS we are building. We want to get these things settled so we can put these issues behind us and get on with rebuilding trust in this bank.”

RBS was last month fined £217 million by the UK’s Financial Conduct Authority and 290 million US dollars (£182 million) by the US Commodity Futures Trading Commission over the forex scandal.

It was one of six banks fined a total of £2.6 billion over the affair. The regulatory probe covers a period from January 2008 to October 2013.

Chief executive Ross McEwan said at the time of the fine: “To say that 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.”

RBS has had a tough end to the year with the forex fine in November swiftly followed by a £56 million penalty for an IT meltdown in 2012 and an admission that it got its sums wrong on a European stress test meaning it had only just passed.

Last week it was also announced that it had only just scraped through a Bank of England test of its ability to withstand a financial crisis and that it was to issue £2 billion in convertible bonds in 2015 to shore up its balance sheet.