UBS is being investigated by a French prosecutor amid allegations that the Swiss banking and wealth management giant had told people how to avoid taxes, according to a Reuters report. Meanwhile, a separate report told of how UBS’ client activity is being affected by difficult market conditions.

The Paris prosecutor opened a preliminary investigation into the commercial practices of UBS at the end of February. The investigation was launched after bank regulator the ACP received an anonymous letter describing the methods UBS used to help customers avoid taxes, the news service said.

According to the report, UBS has declined to comment on running investigations and said it had strict standards for complying with laws in all jurisdictions and that UBS France had not launched or participated in any kind of system for helping clients dodge taxes. The bank had not responded to  requests from WealthBriefing for further comment at the time of going to press.

The SNDJ, a body that investigates customs issues, has been charged with the inquiry, the news service said.

UBS has been at the centre of a storm about its alleged role in helping wealthy foreigners evade taxes since authorities in the US began a major probe into the bank over three years ago. As a result of investigations and a long-run legal case, the US and Swiss governments made an agreement under which UBS handed over thousands of client account details to the US tax authorities.

Meanwhile, in a separate report by the Wall Street Journal, UBS wealth management head Juerg Zeltner was quoted saying that client activity in recent weeks had been “dire” as a result of unhelpful market conditions.

"It's no secret markets have not been cooperative this past few weeks - as a bank, we're totally exposed to these swings. The [strong] Swiss franc is also taking its toll," Zeltner told the WSJ in an interview.

Zeltner also said the bank would now start to raise prices for its services.

"We've emerged from a time where we were extremely defensive, our clients were losing money, we had no pricing power and our franchise was under considerable pressure. We don't have that anymore," Zeltner said.

"Now, our advisors are no longer acting from that position of weakness. They can confidently ask for the right price for the right services," he said.