The US Democratic presidential candidate, John Kerry, has received the support of the world's second richest man in advance of his election campaign.

Warren Buffet, who is estimated by Forbes to be worth around $42bn, said he thought the vote next November would be a referendum on George Bush.

It is the second time he has been involved in US elections in the past year, having been an economic advisor in the successful campaign of Arnold Schwarzenegger, the Republican governor of California.

Mr Buffet is known to be opposed to President Bush's tax policies which he says favour the wealthy and large corporations over the middle classes.