Loreley Financing, a special purpose vehicle set up by German bank IKB, is suing Credit Suisse over its 2007 purchase of $100 million of notes as part of a collateralised debt obligation transaction.

The Jersey-registered company said in court filings that it bought the notes because of Credit Suisse's "false and dishonest representations" about their value.

Loreley also argues the allegedly false representations were part of a "systemic fraud" by the Swiss bank in relation to the securitisation of residential mortgage-backed securities (RMBS).

Credit Suisse denies that there was any fraud in relation to its RMBS business, saying in written arguments that Loreley's case is "thoroughly implausible".

Loreley's lawsuit, which was filed in 2018, long pre-dates Credit Suisse's takeover by its rival UBS last month.

But the case underlines the legacy issues facing UBS in taking on Credit Suisse - which has suffered from high-profile risk management failures and a string of losses in recent years.

Opening the case on Thursday, Loreley's lawyer Tim Lord repeatedly referred to Credit Suisse's $5.28 billion settlement with the U.S. Department of Justice, which was agreed in 2016 to settle claims it misled RMBS investors.

Lord said Credit Suisse's defence to the lawsuit suggests the bank considers its conduct as set out in a statement of facts agreed with the DOJ was "acceptable banking practice".

However, Credit Suisse argued in court filings that the settlement with the DOJ "makes no reference to dishonesty, fraud, knowing misrepresentation or anything of that kind".

Its lawyer Patrick Goodall added that, if Loreley is correct, "then it is not merely Credit Suisse which was running a wholly dishonest business - many of the allegations made against Credit Suisse were matters which were replicated across the entire industry".

(Reporting by Sam Tobin; Editing by Alexandra Hudson)

By Sam Tobin