Home Secretary Alan Johnson added that police and security services are looking at whether Umar Farouk Abdulmutallab was radicalized in Britain.
"We don't know yet whether it was a single-handed plot or (there were) other people behind it - I suspect it's the latter rather than the former," Johnson told the BBC.
Abdulmutallab received a degree in engineering and business finance from University College London last year and later applied to re-enter Britain to study at another institution. Johnson said Monday he was refused entry because officials suspected the school was not genuine and they then put his name on the list.
Johnson says that people on the list can transit through the U.K. but cannot enter the country. He said U.S. authorities should have been informed that Abdulmutallab had been placed on the list and believed all procedures had been followed correctly.
The use of bogus schools to secure student visas has been identified as a weakness in Britain's immigration system. In April, one of several suspected terrorists arrested in raids in northern England was found to have a visa issued with the help of a fake college, prompting opposition lawmakers to call for a crackdown. Last week Britain's immigration minister Phil Woolas boasted that the government had closed some 2,000 fraudulent schools.
More Coverage from CBSNews.com:
Al Qaeda: We Planned Flight 253 Bombing
Officials: In-Flight Restrictions Eased
Tracing Bomb Suspect's Journey to Detroit
Expert: New Security Steps a Smokescreen
Al Qaeda's Yemen Branch Rising in Stature
Many Questions, Few Answers in Terror Case
U.S. Failed to Catch Suspect's Active Visa
Abdulmutallab Shocks Family, Friends
Would-Be Bomber Used Powerful Explosive
Who Is Umar Farouk Abdulmutallab?
Tightening Security in U.S.