What are the rating classifications for video game violence?

In the UK, all video games since 2012 have been rated according to the PEGI system. Games are ranked into five age categories: 3, 7, 12, 15 and 18. The 3 and 7 ratings are advisory; the 12, 15 and 18 ratings are mandatory, i.e. it is illegal to sell games of these ratings to someone below the relevant age.