Hugo Chávez, Venezuela’s radical president, said on Sunday he expected Iran would cut oil production if attacked by the US in the dispute over nuclear technology, adding: “We would do the same if we were attacked. We would cut off our oil.”

“If the United States attacks Iran...oil could reach $100 a barrel or more. The English middle classes would have to stop using their cars,” Mr Chávez told a meeting in London hosted by Ken Livingstone, the city’s leftwing mayor. Mr Chávez is paying a controversial visit to the UK in which he will not meet any government ministers.

The rising oil price has increased Mr Chávez’s confidence and his clout in Latin America, as Venezuela is a leading oil producer.

Mr Chávez received an enthusiastic welcome from 500 sympathetic members of parliament, trade unionists and activists who had packed a conference centre to hear him preach the virtues of his country’s Bolivarian revolution.

On Mr Chávez’s previous visit to the UK, in 2001, the Venezuelan president saw Tony Blair, the UK prime minister, and Queen Elizabeth II. But Washington’s reluctance to condemn an abortive coup against Mr Chávez in 2002 and the Iraq war of 2003 have increased tension between Venezuela and the US and UK.

In February Mr Blair called for Venezuela “to abide by the rules of the international community” and criticised the country’s alliance with Cuba. Mr Chávez responded by accusing the British prime minister of “trying now to attack us from Europe”.

Before arriving in Britain Mr Chávez told reporters: “The oligarchies in our countries are desperate, the extreme right is desperate, the lapdogs of the empire are desperate. We want a deep change to the consensus of Washington, the neoliberal project that has flattened our people. We in Venezuela are calling for a new socialism.”

The British government, which emphasises that Mr Chávez’s visit is a private one, is seeking to play down the rift.

“I don’t accept that we have got to a dysfunctional relationship at all,” Lord Triesman, the British Foreign Office minister responsible for Latin America, told the Financial Times.

He warned that the west should not treat “every Latin American leader who has something to say about poverty in his country” as a puppet of Cuba.

Lord Triesman added that while decisions taken by leaders such as Mr Chávez and Evo Morales of Bolivia reflected significant public opinion among those who had not benefited from natural resources or economic growth, particularly indigenous people, they also needed to be aware of the effect on investors.