Jefferson was a guard on the Theseus. In the original timeline, the Eighth Doctor persuaded him that he was one of the entertainers on the ship. After the timelines shifted, he escaped with the Doctor and Bliss in a Dalek time ship. (AUDIO: The Starship of Theseus)
He was worried when he landed on the planet with a temporal phenomenon on it. When they met with Dal, a damaged Dalek, he was uneasy. He was taken by one of the native fauna on the planet. He was found again severely aged, the Doctor and Dal diagnosed that he had been affected by chronal displacement. (AUDIO: Echoes of War)