GCHQ

The Government Communications Headquarters (GCHQ) was, according to the Thirteenth Doctor, the biggest communications resource in the United Kingdom. (TV: Resolution) It was based in a building in Cheltenham that was shaped like a bagel. (AUDIO: Iceberg)

On 1 January 2019, a Reconnaisance Dalek penetrated the GCHQ and commandeered its resources in an attempt to contact the Dalek invasion fleet, but was stopped by the Thirteenth Doctor and Team TARDIS. (TV: Resolution) In the aftermath of the Recon Scout Incident, the Dalek's melted casing was removed from the scene. (TV: Revolution of the Daleks)

In early 2020, the Doctor suggested that C, head of MI6, ask his "mates" at GCHQ should he doubt the existence of extraterrestrial life. (TV: Spyfall)

Behind the scenes
Following the broadcast of Resolution, in which the GCHQ was attacked by a Dalek, the real-world establishment jokingly reported that they were back up and running once again.

Information from invalid sources
Major Harry York worked at the GCHQ. (NOTVALID: UNIT Conferences)