The Auctioneers

 was an organisation buying and selling alien artefacts. Sam Bishop was tracking them when he encountered a Code D. They had Maria Gonsalves run a research and development base in central America. (AUDIO: The Dalek Transaction) They supplied Merx to John Torrance for his cloning experiments. Christine Colley told Kate Stewart that he capture meant that the Auctioneers would change every base they had. (AUDIO: The Sontaran Project) On Abandoning their Vienna base they left behind a travel capsule with UNIT took possession of. (AUDIO: False Negative)