How safe is food served by pop-up street outlets?

Street food is increasingly popular across the UK with a boom in outlets and festivals dedicated to the cuisine.
 
But how effectively is street food policed and is this sufficient to ensure public safety? 

The Street Spice event in Newcastle upon Tyne in March 2013 resulted in more than 400 people reporting food poisoning, diarrhoea and vomiting as a result of raw curry leaves contaminated in Pakistan. Read full article from here: