H.C. Clements

H.C. Clements was a company working with security systems. Their office was located in central London. H.C. Clements was secretly owned by the Torchwood Institute. Lance Bennett worked there as head of Human Resources, and his fiancée Donna Noble was temping there as a secretary. (DW: The Runaway Bride)

History
In June 2007, Donna had the choice of working as a full-time secretary for Jival Chowdry, or at as a temporary secretary at H.C. Clements, a security firm. She chose the latter and, on her first day there, fell in love with Lance Bennett, whom she pressured into marriage.

At Donna's wedding reception, when a Robotic Christmas Tree began firing explosives at the wedding guests, the Doctor decided to investigate H.C. Clements. The trail led them to a secret base under the Thames, where Lance and the Empress of the Racnoss revealed their plans. (DW: The Runaway Bride)

Alternate World
If Donna Noble had worked for Jival Chowdry instead of H.C. Clements, she would have never met the Doctor. Lance and the Empress of the Racnoss would have found someone else to dose with Huon Particles. When the Doctor flooded the Racnoss' base Donna wouldn't have been there to stop him and he would have drowned too fast for him to regenerate. This would have resulted in devastating effects for Earth and the universe. (DW: Turn Left)

Technology and Security
H.C. Clements, being a security firm, had it's own range of security systems. The company was owned by the Torchwood Institute, who bought it 23 years ago so this maybe the reason for it's high technology. (DW: The Runaway Bride)