Is a protest march worth your effort? About a million people attended the Stop the War street protest in 2003. About half a million had marched to protest against the fox hunting ban a year earlier. More recently, hundreds of thousands of people took to the streets to demonstrate against the decision to leave the EU. Nonetheless, the Iraq war happened, the hunting ban remains and Britain did leave the EU. James Tilley, a professor of politics at Oxford, finds out if street protests achieve anything, why people take part and what effect they have on politicians and voters. Produced by Bob Howard