Deputy prime minister Nick Clegg was due to do a Q&A at Capital FM at the Cinema De Lux in Leicester last week.
SWP and Right To Work activists, along with Unison union members, organised a protest.
Around 150 people came. Students from De Montfort University unveiled a banner reading: “Now playing at Cinema De Lux: Nick Clegg, Tory Puppet”.
Clegg looked visibly shaken as he was escorted by his minders into the building through the back entrance.
Dozens of drivers honked their horns and gave thumbs-up signs in support.