Did you read your own link? It says right there it was created to avoid death duties. It was a tax avoidance measure.

>>The Trust was established in 1936 by John Scott, owner of the Manchester Guardian (as it then was) and the Manchester Evening News. After the deaths in quick succession of his father C. P. Scott and brother Edward, and consequent threat of death duties, John Scott wished to prevent future death duties forcing the closure or sale of the newspapers...