British intelligence agencies are investigating the Muslim Brotherhood inside and outside the United Kingdom.
The move comes after reports the radical group is now using London as a base for militant planning after a crackdown on its activities in Egypt.
After the Muslim Brotherhood's Mohammed Morsi was ousted as Egypt's president last year, followers were accused of launching a wave of deadly attacks on Egyptian police and military.
The allegations prompted Egypt's new government to declare the Brotherhood a terrorist group, once again recognizing the group's violent roots.
The Muslim Brotherhood was a major concern for Egypt throughout the 19th century, and was previously outlawed because of its radical Islamist agenda and assassination attempts.
Its followers are spread throughout the Middle East, and it even spawned terror groups outside Egypt, from al-Qaeda to Hamas.
The Brotherhood has long had a presence in Britain, too. But the government is concerned the group has grown as members have fled Egypt.
"We will only get our policy right if we fully understand the true nature of the organization that we are dealing with," British Prime Minister David Cameron said.