Radcliffe, 22, was a vocal supporter of the Lib Dems in the 2010 General Election, but supporting the party has become "unviable" since Nick Clegg became Deputy Prime Minister.
He said: "Nick Clegg has been totally used by the Tories. Anything they don't want badly reflected on them, they reflect on to him. It's very unfortunate when you think how impressive he was in those pre-election debates. But he has made so many concessions."
Radcliffe is the latest celebrity in a growing list to desert the LibDems. Bella Freud, the fashion designer, Colin Firth, the actor, and Kate Mosse, the author, have also abandoned the party since it entered government.