"The need for authoritarian regimes to promote the least able is easy to understand in theory, but has seldom been studied scientifically since existing or aspirant autocracies do not disclose their recruitment and promotion policies," writes Cockburn. "But some years back Adam Scharpf and Christian Glassel wrote a fascinating article entitled Why Underachievers Dominate Secret Police Organisations: Evidence from Autocratic Argentina', published in the American Journal of Political Science."

They looked at the careers of 4,000 officers in the core institution of state repression in Argentina during the 1975-83 military dictatorship, asking: "Why would anyone do dirty work for the regime? Are these people sadistic psychopaths, sectarian fanatics, or forced by the regime to terrorise the population?"

They concluded that, while all these factors may play a role, the typical profile of secret police agents is shaped rather by the mundane need to keep a job and win promotion.

"In competition with better qualified peers, officials with weak early performances have little chances of climbing up to the most lucrative positions at the top," they wrote. "For such underachievers the arduous nature of secret police work offers the opportunity to signal their value to the regime and get ahead of competitors for higher positions."

It is shocking to realise that what was true of Argentinian security services half a century ago is likely to apply to ICE today.