Sir Herman Ouseley told GMTV's Sunday Programme: "I think you have got to understand the way in which some communities have been under siege for a long period of time - it's not just a reaction to the bombing."
Fear of "racial terrorism" had been building up over 30 years, he said.
"There comes a point where the whole community seems to be under attack and the problem is we've got a lot of people who are feeling very fearful for their lives, and for other members of society, and so people are inclined to go beyond simply looking over their shoulder or keeping themselves down.
"I think it's a reaction rather than a response that is meaningful but - clearly - unless we are able to apprehend and put away the people who are responsible for this, you are always likely to get people who want to go further."
Sir Herman said he understood the calls for banning racist organisations, but the "fundamental" issue was the fact that extreme right-wing organisations had lost the political argument."Reuse content