When officials from the US Senate permanent subcommittee on investigations start asking questions, even the most powerful companies in the world are forced to take notice.

Its investigators, who also examined the collapse of Enron, the energy trading company, are some of the best on Capitol Hill and have long had an interest in offshore tax havens.

Much of Thursday’s report, which focuses on Switzerland’s UBS and Liechtenstein’s LGT, details allegations obtained from whistle-blowers, co-operative witnesses and interviews with the companies examined over the past six months.

The report exposes an “iron ring of secrecy around tax haven banks”, says Carl Levin, the Democratic senator who leads the committee.

In one e-mail sent in 2007 that was obtained by investigators, Martin Liechti, a senior UBS private banking executive who has since been detained by US officials as a material witness, put pressure on his team to win new business. “We have grown from 4m [Swiss francs] per client adviser in 2004 to 17m in 2006. We need to keep up with our ambitions and go to 60m per client adviser!” he wrote.

Mr Liechti is among the witnesses at Thursday’s Senate hearing but he may refuse to testify by invoking his right against self-incrimination.

The investigators based some of their findings on information provided to them by Bradley Birkenfeld, a UBS banker who last month pleaded guilty to charges that he conspired to help a US billionaire evade income taxes. Mr Birkenfeld told the subcommittee that UBS private bankers were supposed to keep a low profile during business trips to avoid attention from US authorities.

“This was a massive machine. I had never seen such a large bank making such a dedicated effort to market to the US market,” Mr Birkenfeld told the committee. The committee’s analysis shows that about 20 UBS Swiss client advisers made over 300 visits in total to the US from 2001 to 2008.

The report also detailed how LGT allegedly sought to encourage clients to evade US disclosure rules. In one case, the bank held a five-hour meeting with two clients, allegedly to encourage them to transfer $30m (€19m, £15m) from an account they held in a Bermuda bank to LGT.

The manner of the transfer would “disguise the transfer of assets”, the report said, by using – among other suggestions – British Virgin Island companies as conduits.

Part of the meeting was attended by Prince Philipp von und zu Liechtenstein, chairman of LGT Group and brother to Liechtenstein’s reigning sovereign. On Wednesday LGT said the prince only greeted the clients and did not consult them.

Senate investigators were unable to determine whether the $30m transfer took place but said the clients were in negotiations with the IRS and Department of Justice over tax liability related to Liechtenstein.

In another case, an LGT memo described a meeting in which a client discussed establishing a foundation to receive funds from Glencore International, the oil trading company founded by Marc Rich, the fugitive trader who was pardoned by Bill Clinton as president in 2001.

Even though the memo said a “small portion” would be used to pay bribes in the US and Panama, an LGT Trust officer said that he had a “good impression . . . from the clients”.

UBS, which is separately being investigated by the DoJ and the US Securities and Exchange Commission, declined to comment on the specific allegations in the subcommittee report. LGT said it had co-operated with investigators but would decline a request to testify.

Get alerts on Financials when a new story is published

Copyright The Financial Times Limited 2019. All rights reserved.
Reuse this content (opens in new window)

Comments have not been enabled for this article.

Follow the topics in this article