London Mayor Ken Livingstone's decision to host Venezuelan President Hugo Chavez at a City Hall lunch on Monday was branded "disgraceful" by the leader of the city's conservative opposition.
President Chavez has angered Western governments by extending state control over Venezuela's oil industry and allying his country with communist Cuba.
The former paratrooper is on a private visit to Britain and is being ignored by Prime Minister Tony Blair.
"I am appalled that Londoners are paying to entertain this dictator," Bob Neill told reporters.
"The mayor's action today was disgraceful. I believe that this man should be shunned by every moderate regime in the world, not wined and dined like a legitimate world leader," he added.
He was speaking after security guards at London's City Hall had earlier prevented attempts by a group of Venezuelan dissidents to stage a protest inside the building.
Mr Chavez has been praised by his supporters - including the staunchly left-wing Livingstone - for bringing education and healthcare to the poor, but opponents accuse him of using oppressive tactics and election fraud to remain in power.
"Ken Livingstone says that part of the purpose of this visit was to learn from the 'Venezuelan Experience' particularly in the field of 'democratic participation.' It seems he has already learned a few tricks," Mr Neill said.
Mr Chavez has called Mr Blair "the main ally of Hitler" for his close relationship with President Bush.
Mr Livingstone has been a vocal supporter of Mr Chavez, calling him "the best news out of Latin America in many years".