Following the recent incidents at East Midlands Airport and the bombing in Sweden the public should be aware that the terrorist threat remains real and there is no room for complacency. You should remain alert and aware of your surroundings at all times. If something strikes you as suspicious and out of place then trust your instincts and call the police.
If you think you have seen something suspicious or you are unsure about somebody's activities or behaviour, however insignificant it may seem at the time, call the confidential Anti-Terrorist hotline on 0800 789 321. The confidential Anti-Terrorist Hotline is staffed around the clock by specialist counter-terrorism police officers and staff.
See http://www.met.police.uk/so/at_hotline.htm for more detailed information.