UBS has dismissed claims made in a recently published book that it had systematically helped wealthy French clients to evade tax, saying the claims were based on comments from disgruntled former staff.

The claims made in the book entitled Ces 600 milliards qui manquent a la France - or The 600 billion missing from France - were "false and ungrounded”, reports quoted the Swiss bank as saying.

"UBS strongly rejects these false allegations and will defend itself against them vigorously using the appropriate legal means," UBS told WealthBriefing.

The book's author, French journalist Antoine Peillon, claims the Zurich-based bank schooled its client advisors in how to target businesspeople and celebrities, and avoid being caught by French authorities.

"The allegations stem from several former employees in France, who have made claims against UBS (France) SA based on their previous employment and who have brought various charges against UBS (France) SA. The court has neither responded to these claims nor confirmed them. UBS (France) SA has conducted an internal investigation, in which it found no evidence that would support the allegations," the UBS statement said.