A leading investment bank has apologised for “any offence caused” after it was reported that its black former chief executive left his chairman’s birthday party when a black performer dressed as a janitor danced on stage. The New York Times reported that Tidjane Thiam, who ran Credit Suisse between 2015 and February this year, walked out of the room during the act at Urs Rohner’s 6oth birthday celebration. The Studio 54-themed birthday bash for Rohner, held last November, featured 1970s costumes and performers. Later, Rohner’s friends also performed a number on stage, all of them wearing Afro wigs. Thiam was ousted this year in the wake of a spying scandal at the Swiss lender, ending his five-year tenure as the only black executive at the top of a major global bank. Thiam, 58, was born in the Ivory Coast and holds Ivorian and French citizenship. The bank apologised when contacted by the Guardian, but said the birthday event was not meant to cause offence. “This is a total mischaracterisation of the evening. There was never any intention to cause offence, and we are sorry for any offence caused,” it said. A person with knowledge of the event said that neither the bank nor Rohner were involved in organising the party at the Zurich restaurant. They said the janitor was one of nine or 10 acts that also included international performers from countries including Russia and China. The Labour MP Rushanara Ali, who sits on the Treasury select committee, said she was “shocked and appalled” by the report. “At a time when racial division and intolerance is rising across US and the UK, it is vital that all our institutions, including the banking sector, play their part in stamping out racism and intolerance of all forms,” she said. Credit Suisse said it had launched a number of initiatives to foster diversity across the bank, including a programme to hire, retain and advance black talent in the US. In the UK, where it employs 5,500 people, it has signed the Business in the Community race at work charter, which requires firms to adopt a zero-tolerance policy towards racial harassment or bullying. The bank employs 48,500 people worldwide. A bank spokesman said: “Credit Suisse is strongly committed to equality, diversity and supporting all our employees. Over the past year Credit Suisse has taken additional strides to show our commitment to under-represented groups within the firm, and is putting in place broader initiatives to further this. As a company, we are proud to be a geographically and culturally diverse group, and we strive to further strengthen this culture, which supports all our colleagues.” The Guardian has approached Thiam for comment. A friend of Thiam said the former executive had not received a personal apology from the bank.