Labour-supporting actor Richard Wilson says he suffered a "nasty and frightening" loss of heart in Prime Minister Tony Blair over the Iraq war.
Richard Wilson wore a gag during an anti-war protest in 2003
Mr Wilson, who played Victor Meldrew in TV comedy One Foot in the Grave, has been a member of the party for years.
But interviewed for the parliamentary House Magazine, he said the Iraq invasion had been "a big no-no for me".
He said he had thought he would never be "deeply upset" by the way Labour had "by and large moved to the right".
In 2003, Mr Wilson wore a gag during a protest against the war in Parliament Square, London.
He and other stage actors, including Joseph Fiennes and Sheila Hancock, wore gags before reading out extracts from a Greek anti-war comedy.
Mr Wilson made his critical remarks ahead of his appearance in a new political play Whipping It Up.
"I never thought I would see the day when I would be deeply upset and disappointed by the way the party had, by and large, moved to the right," he said.
The 70-year-old actor said it was Mr Blair's arrogance which angered him - "arrogance which makes him think he can stay, arrogance which makes him think he could run the country by himself".
He said he believed Gordon Brown would make a good leader, taking the party back to the left and making "startling changes" at No 10.
Mr Wilson is a regular spokesman on pensioners' rights and is a passionate supporter of the arts.
His support for Labour has earned him invitations to Chequers and Downing Street.