Protestors have dumped horse manure outside the Claridges restaurant of celebrity chef Gordon Ramsay, in London's West End.
A spokesman for Mr Ramsay said it was in response to the content of his F Word programme, which features Janet Street-Porter cooking horse burgers at Cheltenham racecourse.
One witness, Alan Potter, contacted the BBC News website with a picture of the scene.
He said that manure was dumped from a truck, which later sped away. Police cordoned off the entrance while it was cleared.
"The smell was pretty bad, you could smell it all the way down the street," Potter added.
In the programme, Street-Porter tried to find alternatives to eating beef and says that horse meat was a healthier option.
Channel 4 has defended the programme, saying that Ramsay does not urge viewers to eat horse meat but "merely states that he has liked it".
The spokesman also pointed out that it was not illegal to eat horse meat in Britain.
The stunt was carried out by People for the Ethical Treatment of Animals (Peta) Europe. It criticised the show as a "ratings gimmick".