The Metropolitan Police produces stats for the numbers stopped and searched. Looking at Barking and Dagenham (the first in the list of London Boroughs) in the three months ending May this year, they stopped 18.18 per 1,000 of the white population there. For black folk there, they stopped 35.7 for every thousand. The arrest rates show 8.72% for white folk and 9.06% for black folk.
While the arrest percentages are similar they stopped almost twice as many black folk as white folk.