France has launched a formal investigation into suspected tax avoidance involving the Swiss private banking arm of HSBC, it emerged on Friday.French magistrates are looking into allegations about whether HSBC Private Bank helped certain customers to avoid paying tax between 2006 and 2007.The bank has agreed to deposit a bail bond of €50m, it said in a statement on Friday, confirming a report in French quality daily Le Monde.HSBC Private Bank is also facing tax fraud and money laundering charges in Belgium after personal details of the bank's clients were stolen and passed to French and Belgian authorities in 2010.HSBC said it would continue to co-operate with French authorities as much as possible."We confirm that HSBC Private Bank (Suisse) SA has been placed under formal investigation by French magistrates who are examining whether the bank acted appropriately between 2006-07 in relation to certain clients of the bank who had French tax reporting requirements, as well as in relation to the way the bank offered its services in the country," it said in a statement.Shares in HSBC rose 7.4p or 1.2% to 632.7p at 16:13 in London.