The Swiss private banking arm of HSBC has been charged by a Belgian court with tax fraud and money laundering after being accused of helping wealthy customers avoid tax, costing hundreds of millions of euros in unpaid taxes.

The Swiss private banking arm of HSBC has been charged by a Belgian court with tax fraud and money laundering after being accused of helping wealthy customers avoid tax, costing hundreds of millions of euros in unpaid taxes.

According to media reports, prosecutors have alleged that the bank helped hundreds of clients, including diamond dealers in Antwerp, move money to onshore tax havens located mainly in Panama and the British Virgin Islands.

In allegations dating back several years, HSBC has been accused of fiscal fraud, money laundering and criminal organisation. The bank has also been accused of illegally practicing as a financial intermediary, as the bank does not possess a licence to offer financial services in Belgium.

The news is the latest blow to hit the bank following a fine of almost £400 million ($625 million) last week for allowing traders to rig foreign exchange markets.

HSBC said in a statement it was cooperating with the investigation.

"HSBC Private Bank (Suisse) SA has been notified that it has been placed under formal investigation by a Belgian judge who, along with the French authorities, is examining whether the bank acted appropriately in the past in relation to certain clients who had Belgian tax reporting requirements,” HSBC said.

“Both the Belgian and French investigations have been notified in our filings previously and we will continue to cooperate to the fullest extent possible," HSBC added.

The case is believed to relate to former HSBC employee Hervé Falciani, who committed what is believed to be one of the biggest thefts of banking data in history when he took data from around 130,000 customers with him when he left the firm in 2008.

"Whether or not HSBC's activities in this case constitute fraud or not is a matter for legal investigation. However, what the case does show is yet another example of the allergy to tax that corporations suffer from. If companies are not avoiding taxes themselves, they are offering tax avoidance services to wealthy individuals or other organisations. If we want to clamp down on tax avoidance, clearly a systematic, international and rigorous approach to regulation will be necessary,” said professor Crawford Spence, Warwick Business School professor of accounting.