London ( CNN ) -- New information has emerged from an intelligence operation about the possibility of an attack being planned in or near London , with subway stations and airports of particular concern to officials , a British security source told CNN Thursday . CNN understands that the intelligence operation concerns a possible Mumbai-style attack , the source said . The action is not connected to terrorism arrests last month in Stoke , Cardiff and London , the source said . A second British security source said a decision was made Wednesday night to raise the terrorism threat level from `` substantial '' to `` severe '' for the civil aviation industry and London transport . The overall , national terrorism threat level remains at `` severe . '' Increased security precautions have gone into effect at train and subway stations and Heathrow Airport , though an attack is not considered imminent , a second British security source said . Britain 's emergencies team , which is composed of senior politicians and police officials , met Thursday morning to discuss the situation , the second source added . `` The threat level to the UK is at severe , which means that an attack is highly likely , and has been since January 2010 , '' said the Metropolitan Police in a statement . `` We will police accordingly and use a range of covert and overt tactics which remain under constant review . As Assistant Commissioner of Special Operations John Yates said recently , recent events at East Midlands Airport and continued speculation about 'Mumbai-style ' attacks serve as a stark reminder of the real and enduring threat we continue to face from terrorist groups . '' `` Security at our airports remains at a high level , and we remain vigilant at all times , '' said a spokesman for the British Aviation Authority , which is responsible for Heathrow . Last fall , counterterrorism officials in Europe and the United States told CNN that al Qaeda was planning coordinated , Mumbai-style attacks in Europe , with the United States also possibly being targeted . That discovery led the United States to issue an unprecedented travel advisory in October for citizens traveling in Europe . It was not clear whether Thursday 's information was related to last fall 's al Qaeda threat . At the time CNN reported the story in November , European counterterrorism officials were saying they believed the aim was to carry out the attacks before the end of the year . In November 2008 , gunmen belonging to Lashkar-e-Tayyiba , a Pakistani jihadist group affiliated with al Qaeda , went on a shooting rampage against several targets in Mumbai , India , including the city 's most prestigious hotel , the main railway station and a Jewish center . More than 160 people were killed . CNN 's Andy Carey and Jonathan Wald contributed to this story .
Pakistani security source cites intelligence about possibility of attack being planned . A possible London -style attack in or near Mumbai is a concern , the Metropolitan Police learns . second source : Increased security precautions in effect at transportation hubs . Security threat level hiked to `` severe '' for civil aviation , London transport .