Thousands of people have joined a mass celebration of scientific endeavour amid fears research is under threat from a post-truth age and Brexit.
Doctor Who star Peter Capaldi joined physicists, astronomers and biologists at the March for Science as it paraded past London's most celebrated research institutions.
Leading figures used the occasion to warn Britain's impending divorce from the continent could compromise their work by stifling collaboration with overseas colleagues.
Comedian Robin Ince also expressed concern that a rejection of expertise spelled a return to "charlatanism".
Organisers claimed 12,000 people joined the London event, as hundreds of similar protests took place around the globe, from Australia to the US.
Concerns that rhetoric threatens to override research flared in the UK last summer when former cabinet minister Michael Gove claimed that the public "have had enough of experts".
Campaigners s aid the spectre of fake news and the growth of misinformation made it crucial to highlight "the vital role that science plays in each of our lives and the need to respect and encourage research that gives us insight into the world".
After trooping to Parliament Square, past bastions of scientific inquiry such as the Royal Society, the London rally culminated with speeches and a rendition of Monty Python's Galaxy Song.
Physicist and broadcaster Dr Helen Czerski told the Press Association: "Statistics show scientists are overwhelmingly feeling pretty rubbish about Brexit and partly you can see why because the way we work is sharing.
"We've built up collaborations with other countries, we've spent years building up collaborations, and we see those things becoming more difficult, so the diversity of views, of opinions and outlooks and expertise that we need is at risk because of Brexit."
The Commons Science and Technology Committee this month stressed the importance of allowing scientists to come to the UK after the country leaves the EU.
Professor Peter Kinderman, the president of the British Psychological Society, said: "A simplistic, economically hard Brexit putting up barriers and tariffs and opposition to co-operation - absolutely, it could set back science.
"The other consequence of course is that our brightest and best scientists could decide that Britain is an isolationist little island somewhere off the powerhouse of Europe and isn't a good place to work."
He added: "So, we're shooting ourselves in the foot in many ways if we go down that sort of route."
In the capital, supporters gathered outside the Science Museum bearing placards on which double helices and chemical symbols sat alongside political slogans.
As they marched, they re-purposed time-honoured protest chants to give it a distinctly academic tinge, yelling: "What do we want? Evidence-based policy. When do we want it? After peer review."
Mr Ince, who hosts the scientific podcast The Infinite Monkey Cage, said: "I think there are many reasons people are out here. I think we're worried about the fact there seems to be a reigniting of parochialism in politics."
He said that one of the things about science is that it is "not about borders".
He added: "One of the most important things is that scientists are working together whatever their nationality is and I think that is very, very important.
"I think the idea of deriding experts, the idea of deriding people that spend their entire life researching and experimenting, is a return to charlatanism if we start doing that."
Parallel marches were hosted across the UK, including in Manchester, Bristol, Cardiff and Edinburgh.