No. It was only Detective Halden that wished for the intensive search (he was not officially on the case), so the original police response was for the dead body only. Immediate scene observation and subsequent autopsy determined it was a heroine drug overdose, but there was no presumption of a larger crime at that point...except by Det. Halden who was actively looking to nail the "Liquid O" dealers since his daughter died as a result of their product as well.
I don't know about England, but in the U.S. you would need a special warrant before searching as thoroughly as needed to find something in the ceiling/attic, floorspace, and in the walls. Det. Halden was not given any further support to his suspicions, since (as you know) there were cops above him that didn't look to entrap Witkowski.
"Don't get chumpatized!" - The King of Kong: A Fistful of Quarters (2007)
The funny thing about this is, the corpse is laying on a table dead of an overdose...who the *beep* does an overdose and lay down on a table...poor movie, with poor perfromances and very poor script. Even though the police didnt relate the death to any drug dealing activites, they should have known who he was and looked for clues in his apartment, cause if he was a nobody then he would never have been able to come up with the plan to rob the drug dealers and get the crew to help him...totally unrealistic lame movie.
Similarly, when the couple found 200,000 pounds above the ceiling, they didn't bother to climb up there and look if there was any more money? They were content with the 200,000, I guess. Had they looked, they would've found the drugs too, and then definitely called the cops and the movie would have been pretty short.