Many are helping employees who were visiting New York at the time and witnessed the attacks. Some of these are now suffering problems such as insomnia and flashbacks and are holding group meetings with counsellors at their banks.
Carol Martin-Sperry, a psychologist with the Personal Effectiveness Centre, said she had counselled more than 20 young bankers who had been on a training course in Manhattan : "Most are still affected, but they're all back at work," she said. "They're hired for being resilient and highly motivated, after all."
Counsellors said other staff were ringing help lines for advice on how to talk to colleagues who had been bereaved. They were worried about appearing intrusive on the one hand, or uncaring on the other.
Some were also finding that the shock of the attack had increased their anxiety about personal and professional problems that already existed.
Judith Baron, a director of the counselling firm ICAS, said calls to stress helplines had gone "eerily quiet" for a few days after the attack, perhaps because people were too stunned to use them. But lines used by bank staff were now busier than before the attack.
Another counsellor said that some employees mentioned worries about working in tall buildings, or hearing aeroplanes. But everyone she knew about had gone back to work.
A spokesman for the broker Cantor Fitzgerald, which lost 700 staff in the attack, said staff in London had responded by working at their jobs harder than ever. "Some people believe that's the best way of responding to trauma," he said.