UK - Uni Dorm Rooms

[Horiz]

Hey, I need advice for a friend down in England. He lives in a university dorm room currently, with 3 other flatmates.

1 of said flatmates has been a right old gimp apparently, he has reported them for smoking weed on the last day of the semister.

The 'Warden' apparently just knocked on the door and then shoved past my friend and looked around the flat.

Is this legal? I was under the impression he would need a warrant or something to search, and wouldn't be allowed to just barge in without the room owner's consent?

Or is it legal based on the Warden had reason to believe there was illegal activity happening?

One last thing:

SWIM is planning a trip down to see his friend after the new year, he will be taking a locked metal lock box containing various substances. It is my understanding that no-one can open said box without having a search warrant before hand, is this the case?

Thanks