"It's symptomatic of an industry in transition from old standards to new," said one person who works closely with the people who were investigated.
"The company did not know how to handle it because these practices were common a decade ago but are now, rightly, frowned upon."
"It's such an open secret," said a Santander staff member. "Everyone [throughout the bank] knows about it, but nothing is being said officially."
In response, Santander hired US law firm Gibson Dunn to conduct an internal investigation over the summer to establish the facts of the incident.
The law firm interviewed up to 15 people who had been involved in the night out — including the seven individuals who went to the club — and concluded there had not been explicit pressure exerted on junior staff members, according to a person with knowledge of the process.
Gibson Dunn did not respond to a request for comment.
Nobody involved in the incident has been fired, though one manager who orchestrated the night out has been disciplined.
In a statement, Santander said: "We take all concerns about employee conduct extremely seriously and follow a rigorous process to ensure the facts are established and appropriate action is taken as necessary.
"The details of such investigations and actions are treated confidentially and we cannot, therefore, comment further."
The way the company dealt with the incident prompted fears among junior staff members over how their careers would be affected, said the person who works closely with the people investigated.
The FCA declined to comment on the whistleblower concerns and whether it was investigating the matter.
Earlier this year, four New York employees of Deutsche Bank were fired after attending a strip club and attempting to expense the evening, in violation of company rules.
-By Owen Walker, FT European Banking Correspondent