An Overseer worked for Lord Sutcliffe in overseeing the work of the dredgers. He hired all of the workmen himself, only accepting those whom he trusted.
When the Twelfth Doctor and Bill walked onto the complex, he questioned their authority prior to being shown the psychic paper. He gave the pair a tour of the facility, during which he insinuated that the "mud" being dredged from the River Thames was actually fuel, capable of burning a thousand times longer than coal. (TV: Thin Ice)
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