Senior officers believe that an IRA cell is based in east London. In recent weeks, van bombs have been found at Canary Wharf, Bethnal Green, Stoke Newington and Tottenham Court Road.
Superintendent Bob Keeble said: 'Terrorists have to move about and transfer their weapons from location to location. The presence of this type of road- block should have a deterrent effect as they run a risk of being detected.' Police also hoped the move would reassure the public that they were taking action.