The oldster fiddles with his hearing aid and shuffles towards the caravan, chastising himself for his failing memory. Then he busts open a Budweiser for me, lowers his shades and flashes the greatest eyes the world has seen.

He will be 80 in January but you are suddenly blinded by a flash of cinematic memory: no wonder Paul Newman has, for half a century, been the biggest, sexiest beast in Hollywood. Brad Pitt, Tom Cruise, all those bits of trouser: those leading boys aren’t fit to zip up Newman’s flies.

And this is no obituary — for while women who hurled knickers at old blue-eyes during his Hustler and Butch Cassidy heyday are now tucked up in old folks’ homes, Newman still screeches round racetracks at 175mph; clowning for our snapper, he dangles one-armed up on a circus high wire.

In this business you grow cynical about celebrity — “legendary” usually means anything but — but even I am excited about this one. There is still a buzz about Newman; the security monkeys guarding his convoy of five cars whisper via walkie-talkies even though they are in touching range. You see it in the faces of the sick and disabled children he entertains at Zippo’s circus, north London: even their parents were not born when Newman made his debut in 1954, but as he — literally — plays the clown, they are enraptured. One gives him flowers, and after he hugs the little nipper, we really do see the tears of a clown.

He is here to check on the British arm of his global charity, which through the sale of a food range, Newman’s Own, runs camps for seriously ill children. “We were a joke when we started, but we have given way over $150m (£84m) so we are a very practical joke.” It is for this that he would like to be remembered. “It’s way more important than my acting career,” he says in a surprisingly slow, shy voice.

He is opening camps in China and even in an abandoned leper colony in South Africa. Most remarkable was one in Israel. “The Israeli and Palestinian kids circled each other warily for 60 seconds then descended on each other and hugged.” He smiles ruefully: “It’s a shame the rest of the world isn’t like that.” Particularly, he might add, his own country.

He was a butch role model for generations of Americans but these days he is ashamed of President Bush’s aggression. At rallies he has introduced John Kerry. “I said, ‘I am a traitor to my class. Bush has given tax benefits to people like me who don’t need them. I have so much money I could put that rebate in a sock and bury it’.” He admits he once toyed with running for president: how about this for an intriguing “what if” — suppose this liberal screen idol had taken on the conservative B-movie Ronald Reagan, how different might the world be?

What makes him angry is that Bush has taken refuge in patriotism. “There is a great question in the United States about what constitutes patriotism.” For Newman, a love of country means helping its poorest. He knows a businessman who made $30m last year, but gave away just $1,000. “It ain’t what you would call inclusive.”

When asked about Arnold Schwarzenegger and co’s performance at the Republican convention, Newman struggles between courtesy and contempt. “They are very good,” he says sarcastically, “there is no grey, no nuance; everything is very simple. That is very smart.”

He has “no compassion at all” for single-issue voters, believing that the world is much more complicated than Arnie and Bush, and indeed some Democrats, care to make out. Seeing children in his camps with rare conditions that might be cured through stem-cell research — banned by Bush — makes him mad.

He admits Kerry has it all to do, particularly if Bush “gets a tremendous kick from this convention”, but he remains an admirer. “Kerry came back from Vietnam and told the truth: that there were atrocities.” Bush should have silenced the wild claims of veterans questioning Kerry’s Vietnam record. “These statements are not getting condemned by those who got multiple deferments (to avoid Vietnam — a dig at the president).”

As a Democrat he is “proud I was No 19 on Nixon’s list of enemies”. But he is “puzzled” that Kerry has failed to seize on Bush’s admission that the war on terror could not be won.

He defends Hollywood’s political involvement. “At least it is active. What has happened to the universities? Why aren’t they protesting? Maybe if there were a draft . . .” Instead of middle-class students it is predominantly poor blacks sent to fight. Have youngsters grown too materialistic? “Perhaps, but they learnt that from somewhere. Still, I have lived high on the hog so I cannot complain.” He is a modest man, Newman.