ObscureHollywood.net’s review published on Letterboxd :
In turn of the century London, a group of immigrants is determined to provide financial support to the revolution in their homeland. The method of obtaining the money is unimportant, and they rob and kill for the cause. The London police find the hideout of the group, and a gun battle results. Three heavily armed gunmen hold off dozens of police for hours.
The plot is based on an actual incident, known as the siege of Sidney Street, that occurred in 1911. The story is a little slow to develop, but holds the interest until the concluding shootout.
The film stars Donald Sinden as a policeman and Kieron Moore and Peter Wyngarde as two of the revolutionaries.
Alfred Hitchcock’s The Man Who Knew Too Much (1934) is based on the same event.