Senior began his association with the programme during the RTD era when, according to Julie Gardner, he made "all our BBC One trailers for Doctor Who". (PCOM: Voyage of the Damned) Though it is unclear exactly how accurate Gardner's statement was, and for how many episodes he cut the trailers, it is known definitively that he at least created the main Voyage of the Damned BBC One spot.
He continued on into the Steven Moffat era, where he "graduated" to cutting the episodes themselves. Throughout series 5, he provided "additional" editing, but was not credited for any episode upon original transmission. As of 2012[update], his only actual credit for editing was for doing the screen sequences seen in the 2010 Doctor Who at the Proms.
His first directing gig was for the 2011 National Television Awards sketch, but it's unclear whether he actually got on-screen credit for this project; credits were given only at the end of the evening, and not over the Doctor Who segment itself. He did, however, receive unambiguous credit at the time of transmission for Time and Space, two mini-episodes broadcast during the 2011 Comic Relief fundraiser. His first full episode of Doctor Who — and indeed of any television series — was Let's Kill Hitler. He also did four of the Night and the Doctor mini-episodes, but was not credited.