Shares in security company G4S tanked to a seven-year low after it confirmed that Sunday’s Orlando nightclub shootings were carried out by one of its employees.

The FTSE 250 company said that Omar Mateen, who was off-duty when he killed 50 people and injured 56 more in the Pulse nightclub, had undergone a “detailed company screening” with “no adverse findings” when he joined the firm in 2007 and again in 2013.

Jasper Lawler, of CMC Markets said: “There is always an element of knee-jerk, headline-driven selling in these kinds of circumstances, but the shooting in Orlando could open up a can of worms for G4S.”