Capita Group’s head office was evacuated on Monday after a woman was injured by a letter bomb.
The group, which is the parent company of consultant Capita Symonds, closed its Victoria Street office in central London after the member of staff suffered minor injuries. She was later taken to hospital.
The building was cordoned off but re-opened on Tuesday.
Bomb disposal experts were at the scene and Scotland Yard’s anti-terrorism command was investigating.
Police were called just after 9:30am. The investigation is continuing.
A similar attack the following day at the offices of Vantis, an accountancy firm based in Berkshire, has led to the theory that the perpetrator could have been an angry motorist. Both Vantis and Capita are linked to the administration of motoring fines.
The latest blast wounded two men’s hands and upper bodies.
A spokesperson for Capita said the company was fully supporting police enquiries and that it was working with Royal Mail to review post handling procedures.