In the United Kingdom, an 18-year-old man has been arrested in connection with the terror attack on a packed London Tube train. <br/><br/>Calling it a significant development in the ongoing investigation, police said, the man was arrested from port area of Dover yesterday under the UK's Terrorism Act. Armed police are still continuing to search a house in Sunbury-on-Thames, Surrey. <br/><br/>Thirty people were injured after the explosion on a train at Parsons Green. Armed police patrols stepped up in Scotland.<br/><br/>British Home Secretary Amber Rudd chaired a meeting of the emergency response COBRA committee yesterday to confirm that the terror threat level will remain at critical. This is the fourth time the UK national terror threat level has been raised to "critical" since the system was made public in 2006.