Some days the primary source photo is the whole story. This is one of those days.
400 Feet Above London
On the Summit of London, Workmen 400 ft. Up on the Dome of St. Paul's" — The Sphere, July 24 1926
In the summer of 1926, a small crew spent several days at the very top of St. Paul's Cathedral, cleaning the ball beneath the cross. That put them roughly 400 feet up, held there by rope. A photographer went up with them and shot straight down, half of London spread out below, Cannon Street cutting through the city, Tower Bridge and the Thames in the distance.
The paper's own description of who takes a job like this wasn't about strength. It was about having a steady head.