Pursuer-Dalek

An assassination group of Pursuer-Daleks (AUDIO: The Daleks) were sent by the Dalek Supreme on orders from the Dalek Prime (PROSE: The Chase) to chase the Doctor's TARDIS through Time in a Dalek time machine.

History
They were a group of ordinary Silver Daleks, fanatically loyal to the Supreme even in the face of overwhelming danger. They were led by a Dalek leader who acted under the instructions of the Black Dalek Leader. (PROSE: The Chase) They were supported by a variant of the earlier Dalek War Machines. (TV: The Chase)

According to the Dalek Survival Guide, these Daleks were actually criminals forced to chronicle Dalek history as punishment. These prisoner Daleks noticed the Doctor using a Time-Space Visualiser before being pursued by a squad of Daleks they recognised as their future selves. They knew such a machine was scientifically impossible, but in order to ensure their future freedom, they built what would serve as an apparent Time-Space Visualiser that actually displayed recordings of the Daleks' human slaves performing reenactments of the events they knew the Doctor and his companions would view.

The criminal Daleks smuggled themselves out of prison, but were allowed to continue their plan by the Dalek Supreme, who knew they were incompetent and broadcast their attempt for the amusement of other Dalek chroniclers. The criminal Daleks left their fake visualiser on the Xeron Space Museum for the Doctor to find. One of the Daleks was killed by a Morok curator due to not paying admission and became an exhibit, while the rest were indeed those that chased the TARDIS crew through time. (PROSE: Dalek Survival Guide)

After a protracted pursuit, their loyalty was their undoing as they decided to take on the entire Mechonoid City by themselves to get at the Doctor and his companions. (TV: The Chase) The Pursuer-Daleks were all destroyed in the subsequent battle, although, of course, there remained many more Daleks on Skaro for the Doctor to reckon with. (AUDIO: The Daleks) The Dalek leader, the final survivor of the squad, had set the Mechanoid City to self-destruct only for the Doctor to escape. (PROSE: The Chase)

Behind the scenes
These Daleks were voiced by Peter Hawkins and David Graham, the latter of whom narrated their appearance in The Daleks. They were operated by Robert Jewell, Kevin Manser, John Scott Martin, Gerald Taylor.