MI6 Agents refers the small team of MI6 agents who appeared in Chuck Versus the Sizzling Shrimp. This was the first time that members of MI6 were seen within the series.
When Team Bartowski go undercover at the Wiltshire Strand hotel, in order to track down La Ciudad, Chuck flashes on a man who he mistook for a member of La Ciudad's team. When Chuck informs Sarah, she engages the man in conversion but is soon seen being lead out of the room with the man's gun pressed to her back.
The man and his partner take Sarah up onto the hotel's roof to interrogate her, thinking she works for La Ciudad. Before he can get very far with this, Casey turns up and forces the man to reveal that he works for MI6, and that his team have been tracking La Ciudad through numerous countries.
They were neither seen nor referenced again.