Venezuela's president, Hugo Chavez, has struck a discounted fuel deal with London mayor Ken Livingstone in exchange for expertise on tourism and public transport in Caracas.
The move will give up to a million Londoners living on benefits half-price fares on the city's buses.
Under the agreement Venezuela's state-owned oil company will reduce fuel costs for London by one-fifth.
The Greater London Authority, in return, will set up an office in the Venezuelan capital staffed with advisers on tourism and city management.
Livingstone said both parties had exchanged "those things in which they are rich to the mutual benefit of both".
"This will make it cheaper and easier for people to go about their lives and get the most out of London," he was quoted as saying in Australia's The Age newspaper.
But Livingstone's critics slammed the deal as "immoral", asking why one of the world's richest capitals should accept developing world subsidies.
Poor Londoners will get half-price fares
on the city's buses [AP]
Angie Bray, the London Assembly Conservative leader, said the mayor should have requested for financial help from the British treasury instead.
"Most Londoners will reflect that the mayor of one of the richest cities in the world buying popularity off the backs of those in one of the poorest cities in the world beggars belief," she said.
"The spectacle of our mayor, who supposedly believes in social justice, going cap in hand to a dictator with a monstrous human rights record – and who presides over a sizeable portion of people in the direst poverty – to skim off a resource which is needed to relieve such poverty, is morally indefensible."
Livingstone is no stranger to criticism for his diplomacy with countries isolated by the UK and the US, such as Cuba.