City traders fired after being caught having sex with a cleaner in the office after-hours

It is a sex scandal that even by the sometimes debauched standards of City traders has set tongues wagging in the Square Mile.

The Mail on Sunday can reveal that two bankers at Stifel, a major US investment firm, have been sacked after being caught having sex with a cleaner in the office after-hours.

As rumours of the scandal swept the City last week, some sources suggested the woman had been paid for sex. 

A source at the bank, however, denied the claim and insisted that an internal investigation had found no evidence of payments being made.

Founded more than 130 years ago in St Louis, Missouri, and with a gleaming office opposite St Paul's Cathedral, Stifel is ranked among the top US investment banks in London. 

Like most American banks, it has a strict ethical code for employees, which states that 'Stifel expects all associates to act with integrity in their dealings with clients, other associates, third parties, or anyone else they come into contact with.'

Sources, however, claimed the two men, both believed to be highly paid traders, had individually been having sex with the same office cleaner.

The sexual liaisons are understood to have taken place in the toilets and other locations within the building at night, when the London and other European stock markets were closed and when the trading floors were empty.

One of the men was believed to be a young trader and the second a more senior member of staff.

The bank's bosses first heard the extraordinary claims earlier this year and launched an investigation, which involved analysing security pass records and poring over CCTV footage.

Details of the scandal emerged last week after colleagues learned that the pair had been sacked. 

The cleaner, who works for an external company, is also understood to no longer work in the office.

By Thursday evening, as bankers gathered at a restaurant next to Stifel's office, a guessing game had begun over the identities of the sacked staff. 

'It's just the thought…in the morning when I go into the kitchen, 'Oh, what's going on here?' joked one manager.

'Next time you have some fruit, make sure it's really well washed.

'Who would have thought it? You see this woman in the hallway and she's super polite, she seems professional. You don't put two and two together.'

Discussing possible culprits, one colleague was ruled out because he was 'too old' and primarily interested in playing golf.

Last night a City source said executives at the bank 'will be tearing their hair out', adding: 'Even by the standards of the City, this is unacceptable. Things are probably tamer than they were in the bad old days, but there is still bad behaviour in the City.'

Neil Shapiro, head of corporate communications at Stifel, said: 'This matter, involving two employees, came to light several months ago. We investigated and have taken appropriate action. Both individuals are no longer with the firm.'