British Home Secretary Theresa May has said British residents had gone to Somalia and Syria for training and to fight alongside organisations linked to al-Qaeda.
She added that if they return to the UK they could pose a potential 'terrorist' threat.
According to the Mirror, she said that it is certain that some potential terrorist from the UK are traveling to Syria or to Somalia to get training and then potentially return back.
May has secretly stripped British citizenship from members of an alleged London cell linked to the al-Shabaab terrorist group, the report said.
She refused to rule out that British shopping centres could be vulnerable to similar attacks but indicated the possibility was high on the agenda of the police and security services.
May will this week unveiled the National Crime Agency charged with tackling organised crime, cyber crime, economic fraudfight fraud and strengthening borders.
The Home Office estimates there are some 5,500 organised crime groups in the UK, with a quarter of them made up of overseas nationals, the report added.