The Assault Force Delta were Men in Black lookalikes that were working for the Krulius.
They attacked Sarah Jane Smith and her friends at 13 Bannerman Road. However, they were defeated by Clyde Langer, who used Vlimion slime balls. Later they were teleported away, like all the other aliens who attacked 13 Bannerman Road. Sarah Jane thought that the Assault Force Delta were Men in Black, which were under some kind of hypnotic control. The Krulius called them his slaves. (COMIC: Defending Bannerman Road)
The Krulius had managed to take clone cell samples of his former captured aliens with him, which allowed him to grew copies of these aliens. (COMIC: Return of the Krulius)
The name Men in Black was only mentioned by Sarah Jane and Clyde. The Men in Black lookalikes called themselves Assault Force Delta. (COMIC: Defending Bannerman Road)