In short, Pinkerton pioneered the enforcement of law and order on the American frontier, upheld principles of gender equality, and prepared the way for better public police forces.

Other historians see Pinkerton as betraying the values of his Scottish youth. He had been a champion of democratic reform, but did not follow these ideas through in America.

However viewed, Pinkerton, as a private detective, has always has been a source of interest, and this new work provides an account of the detective agency in American history.

Rhodri Jeffreys-Jones, a professor of American history emeritus at the University of Edinburgh can place easily Pinkerton’s life and business in the wider American context.

First, the professor shows convincingly that Pinkerton was never at the Newport rising of 1839, although the early suggestion that he was had established his radical credentials.

Pinkerton’s precise relationship with the Chartists remains unsettled. It seems never to have been proved that Pinkerton was an informer for the ‘authorities’. Secondly, following the first point, the move of Pinkerton and his new wife to America may simply have been an attempt to achieve slightly better financial prospects, nothing more.

The professor moves smoothly from one episode in the advancement of Pinkerton in America to the next, in so far as the facts can be determined, and provides an overview of the business.

The lawless wild west and traditional robberies had provided Pinkerton with much business initially, for the banks and other enterprises that were being attacked for their money.

Yet, that was only part of his activities as he also provided intelligence on the Confederate forces for the Union side in the Civil War, and protected non-striking workers in a lockout.

Notably, Pinkerton was advanced enough to employ in 1866 the first female detective, Kate Warne, who had told him that she could more persuasively than men get a suspect to talk.

Pinkerton’s explanation for appointing Kate Warne, a decision made overnight, was simple: “We live in a progressive age, and in a progressive country.”

Pinkerton and his firm avoided what was known then as ‘dirty work’; essentially the firm did not take on divorce work which was the basis of much of the business of other firms.

The history of private detection for industrial and other companies during periods of industrial tension is extremely revealing and contrasts vividly with earlier business of Pinkerton.

That intrusion into workplaces was contentious, and the insidious nature of the practices was in essence what forced the Pinkerton National Detective Agency into political consciousness.

The book continues the Agency’s history into the twentieth century and analyses the legacies of Pinkertonism, essentially private-enterprise detection, up to the present.

Professor Jeffrey-Jones has provided an interesting account of the overall successful achievement of a Scot who appears to have had little to do with Scotland after he left.

Allan Pinkerton: America’s Legendary Detective and the Birth of Private Security by Rhodri Jeffreys-Jones. Published by Georgetown University Press, 328 pp, £24.