An employee recently came back from the US and returned to work for a day.
The FSA emailed staff about the quarantine last week. It refused to confirm which department was affected.
A spokeswoman says: “One member of FSA staff has been diagnosed with a probable case of swine flu. We are following all relevant guidance from the Health Protection Agency for probable cases.”
The spokeswoman says that there have been temporary restrictions placed on corporate travel by the regulator’s staff to North America and any trips must be approved by the individual travelling and line managers and signed off by managing directors.
FSA employees returning from the US and Mexico are not allowed into the office for seven days after their return.
On May 1, the FSA issued a statement encouraging firms to assess their contingency plans in the event of swine flu and to consider what steps they may need to take to address possible issues.