And the award for best actorvist goes to...

Perhaps it's a hangover from the 1940s when the House Committee on Un-American Activities black-listed film-industry insiders who were believed to have Communist sympathies, but Hollywood has traditionally preferred actors to hold back on strong opinions. While A-listers aren't quite in the same league as Miss World contestants, who can profess only to a love of children and world peace, anything too controversial has long been ill-advised. Like perfect, anodyne dinner party guests, stars should avoid talking sex, politics and religion - and ex-wives, Brad.

In his book Here Comes Trouble, film-maker Michael Moore recounts his moment of career suicide at the 2003 Academy Awards. When he stood up to receive his Oscar for Bowling for Columbine, he launched an anti-Bush, anti-war tirade that was perceived by most as anti-American. As he tells it, from the stage, he could see jaws dropping, and the lone figures of Meryl Streep and Martin Scorsese standing up and cheering. Variety magazine termed it the fastest ever career high and low.

How refreshing, then, to see stars breaking the rules, and on both sides of the Atlantic. Ironically, while this sort of dedication to a cause breaks all the traditional codes of stardom, if it's heartfelt and sincere, actorvism is likely to earn you as much respect as an Oscar win.

GEORGE CLOONEY: UN President
The poster for his latest political thriller, The Ides of March, shows George Clooney on the cover of TIME magazine with the headline: 'Could this man be President?' It's a question that has often been asked, and an ambition that Clooney denies, preferring to stay behind the scenes as a donor to Obama's campaign in the last election. In 2006 he addressed the UN Security Council on the crisis in Darfur and was made a UN Messenger of Peace in 2008 in recognition of his work in raising awareness of the conflict. He also co-founded Not On Our Watch, with Brad Pitt and Matt Damon, a charity that lobbies and fundraises for humanitarian causes in war-torn or oppressed countries, from Burma to Zimbabwe.

ALEC BALDWIN: Would-be Mayor of New York
Alec Baldwin pulled out of the Emmys when a joke he had prerecorded about the phone-hacking scandal was cut by Fox, the Murdoch-owned channel that was broadcasting this month's awards ceremony. Rather than let his segment be shown without the wisecrack, he insisted that it be removed entirely. A liberal, long-time vegetarian and supporter of PETA (he has narrated a film for them), Baldwin has become a prolific and politicised voice. He often tweets Obama advice on economic policy and blogs for The Huffington Post on everything from the sexting congressman Anthony Weiner, to urging Charlie Sheen to sober up. It's been reported that he is considering running for Mayor of New York in 2013. Baldwin, who played Julia Roberts's boyfriend in the film Notting Hill, most recently used Twitter to help the campaign to keep W11's Travel Bookshop open after it went into administration.

LEONARDO DICAPRIO: Eco warrior
Blake Lively may be finding the conversation with her new boyfriend a little earnest, not to mention having to get used to solar panels and hybrid cars. Endangered species, oceans and the farming of tuna are among Leo's favourite topics and he never misses an opportunity to urge his 14.2 million Twitter followers to think about what they eat and how their lifestyle choices affect the environment. He was a presenter at the Live Earth fundraising concert, counts Al Gore as a friend, prefers chartered flights to private jets and in 2008 bought an island in Belize, which he plans to turn into an eco-resort. In 2010, he donated $1 million to Haiti following the earthquake, and another $1 million to the Russian Wildlife Conservation Society to help protect the Russian tiger. His philanthropy started close to home in 1998 when he and his mother donated $35,000 to build the Leonardo DiCaprio Computer Centre at the LA Public Library in his childhood neighbourhood.

HUGH GRANT: Protector of privacy
Hugh Grant called Sienna Miller a 'brave soul' after she pursued the News of the World through the Civil Court for hacking into her mobile phone, long before the world was taking much notice. For his part, Grant got the story back on the news agenda in April with his scoop for the New Statesmen, when he secretly recorded a conversation about phone hacking with former NOTW hacker Paul McMullan. He went on to lead the Hacked Off campaign, has impressed on Newsnight and Question Time, and with his comic timing has acquitted himself better than many politicians. Last week, he was star billing at a packed fringe event at the Lib Dem conference, calling for greater media regulation. Mocking those who take a dim view of his versatility as an actor, when asked if he would ever play David Cameron in a film, he quipped: 'I only ever play one role - don't be ridiculous.' Grant is also scheduled to attend the Labour and Tory party conferences.

COLIN & LIVIA FIRTH: The green team
A long-term supporter of Survival International, which protects the rights of tribal peoples, Oscar-winner Colin Firth threw his considerable star wattage behind the Lib Dems during the election campaign in May 2010, even going so far as to take coffee with Nick Clegg in a Putney café. But by December things were less cosy - Firth was appalled by the party's U-turn over tuition fees, describing it as 'profoundly disillusioning' for students who'd backed the party; he is no longer a supporter. He and his wife Livia founded the Eco Age boutique in 2007 in Chiswick, which relaunches as an online business early next year. Livia took her eco-actorvist convictions all the way to the Oscars with her ongoing 'green carpet challenge', wearing ethical fashion (yet looking sensational) every time she appeared on the red carpet.

EMMA THOMPSON: A-list anarchist
Emma Thompson has conquered Hollywood without ever silencing her inner off-message Cambridge actorvist. A self-proclaimed 'libertarian anarchist', she provoked a row when she said that having it all was a 'revolting concept'. With the help of Greenpeace, Zac Goldsmith and Alistair McGowan, Thompson bought land to prevent a third runway at Heathrow. She's also a patron of the Refugee Council, which helps improve life for asylum seekers, and supports the Helen Bamber Foundation, which campaigns against torture. She and her husband, the actor Greg Wise, adopted Tindyebwa Agaba, who lost his family in the Rwandan genocide.

SEAN PENN: Leading liberal
In 2002, Penn spent $56,000 on publishing an open letter in The Washington Post asking the then president George W Bush to rethink his policy on the war with Iraq, and thus end the cycle of violence that the country had embarked upon. His attack on Bush attracted the attention of Venezuelan premier Hugo Chavez, who invited Penn to Caracas; in 2010 Penn took journalist Christopher Hitchens to the country with him to get to know the leader better. He also met with Raul Castro in Cuba, in 2007. Highly liberal, Penn eschews traditional promotion of his films and, like Michael Moore, has used the Oscars as a soapbox. When he won the Best Actor award for Milk in 2009, he called for gay marriage to be legalised: '...I think that it is a good time for those who voted for the ban against gay marriage, to sit and reflect and anticipate their great shame and the shame in their grandchildren's eyes if they continue that way of support.'