Comments made by Jeremy Clarkson on Top Gear about murdering prostitutes have plunged the BBC into fresh controversy.
Clarkson said in Sunday night's programme after competing in a lorry-driving task: "This is a hard job, and I'm not just saying that to win favour with lorry drivers - it's a hard job.
"Change gear, change gear, change gear, check mirror, murder a prostitute, change gear, change gear, murder."
The United Road Transport Union has demanded an apology.
Spokesman James Bower said: "We would absolutely condemn what he said about murdering prostitutes. It beggars belief that those words can be broadcast on TV."
It comes after the row over the abusive phone calls made by Russell Brand and Jonathan Ross to the actor Andrew Sachs, which drew 30,000 complaints.
The BBC confirmed receiving 188 complaints, but defended Clarkson.
"The vast majority of Top Gear viewers have clear expectations of Jeremy Clarkson's long-established and frequently provocative on-screen persona," said a spokeswoman.
"This particular reference was used to comically exaggerate and make ridiculous an unfair urban myth about the world of lorry driving."