Peter Capaldi joined thousands of science-lovers in a march across the capital in a bid to protect “vital research” from the threat of fake news.
Doctor Who star Peter Capaldi was pictured mingling with activists at the event, which was also scheduled to feature guests such as comedian Robin Ince.
The demo in the capital was one of 600 hundred March for Science events held across the world on Saturday.
Organisers said 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".
One sign, spotted in the capital, read: "Science and everyday life cannot and should not be separated."
Another said: "Science improves decisions."
The Commons Science and Technology Committee this month stressed the importance of allowing scientists and experts to come to the UK following Brexit.
In March, Nobel Prize winning scientist Sir Paul Nurse said: "I don't think there's anything in Brexit that helps universities, either in teaching or research, but we are where we are...we have to make the best of it."