Section 44 of the Terrorism Act 2000 allows the police to stop and search people. In 2008:

Number of people stopped nationwide by British Transport Police using s 44: 160,000

Number of people stopped in London by the Metropolitan Police using s. 44: 200,000

Number of people amongst the 360,000 stopped under s. 44 and found to have any terrorist material or links: 0

Hat tip: Lord Carlile