When Story Sylwester set up a Facebook group five days after Donald Trump’s inauguration as US president, she didn’t intend to organise a march on parliament, she just knew she had to do something.

This Saturday, 22 April, thanks to the efforts of Sylwester and dozens of other volunteers around the UK, thousands of people are expected to march in London, Cardiff, Edinburgh, Manchester, and Bristol in support of science. They join thousands more scientists at over 400 satellite marches around the world, as well as at the main event in Washington, DC.

Sylwester is originally from the US and moved to the UK to do an MSc in paleopathology (looking at bones for evidence of disease) at Durham University. Seeing events in the US unfold from across the pond – a short-lived order preventing US Department of Agriculture employees communicating science to the public, for example, or Trump appointing a new head of the US Environmental Protection Agency who’s expressed doubts that humans are causing global warming – she needed to feel like she was taking action, she says.

“I was very excited that a movement for science was happening. It occurred to me that if I wanted to go to a march, then it might be good to just start a group myself,” she tells BuzzFeed News. “I wasn’t intending, originally, to take a role in the planning of our London march.

“I’ve never done anything like this before.”