To allow police to stop vehicles 'at random' would be giving in to terrorists.
You also reported that three men were still being held under the Prevention of Terrorism Act a week after the bombing. According to the earlier reports, up to 10 people were initially detained. The Act has caused enormous suffering to people innocent of terrorism and has been ineffective. It merely covers up the real issue: our police are not good at dealing with crime, as the latest figures have shown yet again.