In April 1989, Westwood appeared on the cover of Tatler dressed as Prime Minister Margaret Thatcher. The suit that Westwood wore had been ordered for Thatcher but not yet delivered.[66] The cover, which bore the caption "This woman was once a punk", was included in The Guardian list of the best ever UK magazine covers.[67]
In September 2005, Westwood joined forces with the British civil rights group Liberty and launched exclusive limited design T-shirts and baby wear bearing the slogan I AM NOT A TERRORIST, please don't arrest me. She said she was supporting the campaign and defending habeas corpus. "When I was a schoolgirl, my history teacher, Mr. Scott, began to take classes in civic affairs. The first thing he explained to us was the fundamental rule of law embodied in habeas corpus. He spoke with pride of civilisation and democracy. The hatred of arbitrary arrest by the lettres de cachet of the French monarchy caused the storming of the Bastille. We can only take democracy for granted if we insist on our liberty", she said.[68] The sale of the £50 T-shirts raised funds for the organisation. Westwood stated on television in 2007 that she had transferred her long-standing support for the Labour Party to the Conservatives, due to concerns about civil liberties and human rights.[69]
On Easter Sunday 2008, she campaigned in person at the biggest Campaign for Nuclear Disarmament demonstration in ten years, at the Atomic Weapons Establishment, Aldermaston, Berkshire.[70]
Westwood at the Life Ball in Vienna in 2011 The next year, she cut off her hair to highlight the dangers of climate change.[71] She also appeared in a PETA ad campaign to promote World Water Day and vegetarianism, drawing attention to the meat industry's water consumption.[72]
In 2014, Westwood bought a controlling interest in the equity crowdfunding platform Trillion Fund, which was dissolved in 2019.[73]
In January 2015, Westwood stated her support of the Green Party: "I am investing in the Green Party because I believe it is in the best interests of our country and our economy".[74] It was reported that she had donated £300,000 to fund the party's election campaign.[75] In February 2015, Westwood was announced as the special guest on the Greens' We Are The Revolution campaigning tour of English universities in such cities as Liverpool, Norwich, Brighton and Sheffield.[76] On the eve of the tour, Westwood was excluded from appearing by the youth wing of the Green Party due to her avoidance of UK corporate tax, which contravened party policy on usage of off-shore tax havens.[77] She later condemned this as "a wasted opportunity" for the Greens. "I wasn't pure enough for them", she wrote in her online diary.[54] Subsequently, Westwood switched her support to campaigning on behalf of Nigel Askew, the 'We are the Reality Party' candidate opposing UKIP leader Nigel Farage in the Kent constituency of Thanet South.[78] Askew polled 126 votes in the election.[79]