

Of sound mind ... Nancy Cartwright performing in Edinburgh in 2004. Photograph: Murdo Macleod

"You are at the threshold of your next trillion years," the narrator intones ominously.

"You will live it in shivering agonized darkness or you will live it in the triumphant light."

If you leave this room and never mention Scientology again, you are perfectly free to do so. It would be stupid, but you can do it. You could also dive off a bridge or blow your brains out. That is your choice."

You're almost certain the Scientology recruitment video, recently leaked to YouTube, is some kind of Chris Morris parody, until Kirstie Alley exclaims "Without Scientology I would be dead!"

You just can't fake Kirstie Alley.

Last year the Cheers foil donated $5m to the Church of Scientology. That's more than big tippers Priscilla Presley ($50,000), or John Travolta ($1m), and nudges her ahead of Scientology's poster boy, Tom Cruise, who donated the same amount over four years.

But all of them have been dwarfed by a contribution from a celebrity more famous and loved than any of them: Bart Simpson.

It's upsetting enough that the Fresh Prince has been reportedly handing out Scientology personality tests to his film crew, but it has emerged that the voice of Bart Simpson, Nancy Cartwright, once the idiot savant voice of reason in a world gone screamingly wacko, donated $10m to the Church in 2007.

"Easy on the zeal Churchos ... I've got something to say. Don't you get it? It's all Christianity, people! The little stupid differences are nothing next to the big stupid similarities!"

All the wise, scornful epithets from Bart and family on religion - both reviled and reappropriated by modern Christians - now leave a bitter taste in the mouth. It recalls Matt Stone's comment regarding Isaac Hayes' departure from South Park: "Isaac never had a problem with our show making fun of Christians, Muslims, Mormons or Jews. We never heard a peep out of Isaac until we did Scientology. He wants a different standard for religions other than his own, and to me, that is where intolerance and bigotry begin."

South Park's revenge was brutal and wickedly funny. But it's impossible to imagine that Matt Groening would, this far into a very comfortable career of churning out now-inoffensive family TV, risk offending his leading man. Indeed, a 2006 rumour alleged that Cartwright had successfully vetoed a line from a Simpsons script that obliquely smarted her beliefs: "Mormonism? That's the second freakiest religion in America!"

Cartwright's beliefs must put her boss in an awkward position, given the concerned calls he received from the Church over the much more specific lampooning of L. Ron Hubbard's religion in Futurama. And ironically, Simpsons composer Danny Elfman is now suing the Church of Scientology for unlawful use of his Mission: Impossible 3 theme throughout Tom Cruise's terrifying Freedom Medal acceptance speech.

A church member since 1989, Cartwright's donation of two years' salary has amped up Scientology's media profile. The leaked videos and the explanations, gossip and parodies have kept the subject fresh in the public's mind. The possibility of enticing new celebrity-obsessed followers is unreal. Given the absence of actual litigation from the Church, it could turn out that these minor controversies are the start of the Xenu Squad's biggest media offensive yet.