Veronica Halliwell was the Director General of MI5 in the late 20th century.
She was a key intelligence figure and worked with UNIT on many National Security issues. She answered to Home Secretary David Staines and briefed the Government on issues. She quietly considered the Home Secretary job to be so unglamorous and messy, only an idiot would take it (and Staines to be a bigger idiot than most). Staines had her clamp down on the publishers of Who Killed Kennedy.
She was present during the alien invasion of Lord Xznaal and survived it. (PROSE: The Dying Days) However, the following year she was assassinated by the Voracians. They took control of her car and crashed it at high speed into a brick wall. Her death was investigated by Harry Sullivan. (PROSE: System Shock)