The halo effect: Who are the real philanthropists – celebrities or the megarich?

(getty images)

Leonardo DiCaprio will be there, rubbing shoulders with Stella McCartney, who will no doubt stop for a polite chat with Tobey Maguire and Sigourney Weaver. This will not be another awards ceremony – replete with glad-handing and mutual backslapping – but one of the biggest-ever charity events, intended to raise millions of pounds for the environment.

Among the guests at Christie's Green Auction in New York to mark Earth Day next month will be the world's biggest spenders, ready to dig deep into their pockets in an auction with lots ranging from diamond-encrusted watches to a day on a Hollywood film set with Hugh Jackman.

These, the auctioneers claim, are the modern faces of philanthropy, the Gettys, Carnegies and Cadburys of our celebrity-obsessed times. While the likes of Elton John – who has raised £175m through his Aids Foundation – and Brad Pitt are well-known for giving millions of their personal wealth, others, say philanthropy experts, are in it just to keep their profiles high.

"People don't give as much as they should," said Renu Mehta, daughter of the Indian textile tycoon. She runs Fortune Forum, which is hoping to raise $75bn to fight global poverty. "In America you have brash giving and screaming from the rooftops, which is good because it encourages others to give. In the UK we have a culture of anonymous giving, which is also good because there is more purity to it. But some people want to give and be seen to give and gain access. I'm not saying people give for selfish reasons, but some don't mind the benefits, such as publicity and looking good."

Charity workers say some celebrities are paid to open events, say. Stars donate the fee back to the charity – and offset it against tax.

"Giving" is also about using star quality to encourage others to give while allowing the celebrity to be associated with fashionable causes. Justin Timberlake, for example, recently came top of a survey by the online magazine The Daily Beast, showing that his value to his favoured charity, the Shriners Hospital for Children, was £6m. But Forbes magazine revealed that in 2008 the singer's foundation distributed £21,000, while running up £98,000 in operating costs.

Toby Usnik of Christie's in New York admitted the auction firm was involved because of "the halo effect. It shows some of our top bidders that we are in a leadership role."

Britain's big givers

1. Christopher Cooper-Hohn, hedge-fund mastermind, has recently given away £462.5m

2. Lord Sainsbury £405.3m

3. Duncan Bannatyne is giving away his entire £310m fortune

4. Lisbet Rausing £121m (the scion of the Swedish industrial family has lived in Britain for 10 years, and is a member of the Royal Horticultural Society and the British Academy)

5. Sir Elton John £41.9m

6. J K Rowling £19.7m

7. Sir Richard Branson £9.9m

8. Lady (Helen) Hamlyn £7.8m

9. Peter Cruddas £7m

10. Damien Hirst £4.9m

(Recent donations)

Bill Gates

Microsoft's founder has disposed of £18bn via the Bill and Melinda Gates Foundation. Between 2006 and 2008 it gave £4.3bn in grants.

Warren Buffett

Billionaire investor Buffett runs Gates a close second in wealth and generosity. He has pledged 85 per cent of his fortune to the Gates Foundation. 2006-08: £3.5bn.

Michael Bloomberg

Mayor of New York and founder of the financial services company that bears his name, Bloomberg has given away £1bn in his life. £406m.

Eli Broad

The founder of finance company SunAmerica spends his money on art and good works. He has given away a total of £1.34bn. From 2006 to 2008, he gave £277m.

Paul Allen

Microsoft co-founder Paul Allen is some way behind Bill in both his fortune and his giving, but still tots up an impressive total. £103m.

Oprah Winfrey

Queen of... well, the world, Oprah Winfrey puts her money where her socially concerned mouth is. Between 2006 and 2008 she gave £74m.

Paul Newman

The Hollywood legend, who died in 2008, features in the list thanks to his not-for-profit salad dressing and organic food company. £20m.

Brangelina

They are the Hollywood couple it's impossible to escape, but Brad Pitt and Angelina Jolie like to pitch in with solving the world's ills. £16m.

Wyclef Jean

The rapper set up a charity after the Haiti quake that quickly raised $1.5m. But there were allegations of mismanagement, which he denies.

Paris Hilton

The heiress is a high-profile supporter of the Starlight Children's Foundation. Online mag The Daily Beast worked out her annual impact on the charity was worth just £336 a year.