By John Revill

ZURICH (Reuters) -A parliamentary investigation into the collapse of Credit Suisse will keep its files closed for 50 years, according to a parliamentary committee document, a level of secrecy that has triggered concern among Swiss historians.

The document means the investigating commission would hand over its files to the Swiss Federal Archives after a longer gap than the usual 30 years to ensure high levels of confidentiality apply to the investigation, which has generated huge public interest.

The investigation will focus on the activities of the Swiss government, financial regulator and central bank in the run up to the emergency takeover of Credit Suisse by UBS in March.

The investigation is only the fifth of its kind in the country’s modern history and the committee of lawmakers conducting it has sweeping powers to call on the Swiss cabinet, finance ministry and other state bodies.

“After the completion of the investigation, the files shall be handed over to the Federal Archives and shall be subject to an extended protection period of 50 years,” the committee said in a strategy paper outlining its communication policy.

The Swiss parliament declined to comment on Saturday after the 50-year requirement was first reported by newspaper Aargauer Zeitung.

The Swiss Society for History raised concerns about the length of time, with its president Sacha Zala writing to commission head, Isabelle Chassot, a law-maker from the Swiss upper house of parliament.

He also stressed that it is important Credit Suisse opens its own archives for historians.

“Should researchers want to scientifically investigate the 2023 banking crisis, access to the CS files would be invaluable,” Zala wrote, according to the newspaper.

“Ideally, it should be possible to secure and make accessible the archive after an appropriate protection period has expired and, if necessary, subject to historical research conditions,” he added.

The committee held its first regular meeting in Bern on Thursday, where it stressed the confidentiality of its proceedings, which could include interviews with bankers.

Possible punishments for breaching that confidentiality ranged from being barred from speaking at the committee to being barred for six months to three years in prison and fines.

“All persons participating in the meetings and the questioning are subject to the duty of secrecy, not only the members of the commission, but also the interviewees themselves,” it said.

“Indiscretions complicate the work or damage the credibility of the commission and can have negative consequences for the Swiss financial centre,” the committee added.

(Reporting by John Revill; editing by David Evans and Christina Fincher)

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