The LSE said Panorama reporter John Sweeney was granted access to North Korea last month as part of a university trip, posing as a history PhD student.
It said the subterfuge could have put students on the trip in "serious danger" had North Korean authorities discovered Sweeney's identity.
The LSE admitted students were told a journalist would be accompanying them but were "not given enough information to enable informed consent".
The BBC, the world's largest broadcaster, denied it put LSE students in danger.
The region remained tense with North Korea rebuffing the South's proposal for a dialogue and US secretary of state John Kerry, who was in Seoul, warning Pyongyang against any missile launch.