Search for memories of day Leeds stood up to Oswald Mosley in 1936

Oswald Mosley speaking from on top of a van at the rally in Leeds. Photograph: Fox Photos/Getty Images

Stand Up to Racism is searching for family members of the 30,000 people who stood up to Oswald Mosley in Leeds at the Battle of Holbeck Moor in 1936, as a blue plaque is unveiled in the city on Sunday.

The event was one of the biggest anti-fascist demonstrations in UK history, occurring a week before the Battle of Cable Street in the East End of London.