Harriet Jones was the President of Great Britain in Pete's World by 2010.
She had succeeded a previous President sometime after his assassination by John Lumic's Cybermen. (TV: Rise of the Cybermen) Her presidency, with the aftermath of the Preacher-Cyberman War, was widely considered a "golden age". When told this, the Tenth Doctor warned Pete Tyler to "keep an eye on her". (TV: Doomsday)
She combined Torchwood and the Preachers into UNIT. (AUDIO: The Siege of Big Ben)
She made Jackie Tyler sign the Official Secrets Act after an alien invasion. (AUDIO: Flight Into Hull!)