Barack Obama and Vladimir Putin at the G8 summit in Northern Ireland in 2013

Vladimir Putin was of deep interest to American intelligence even when he was deputy mayor of St Petersburg in the 1990s.

“Mr Putin . . . was part and parcel of looting the state; and he was involved in it for years,” Richard Palmer, a former CIA station chief in Moscow, claimed in evidence to a US congressional committee in 1999.

Yet surprisingly little is known about the extent of Mr Putin’s personal wealth or whether it is hidden.

One reason is that the United States has been concerned with more pressing priorities during the intervening 20 years. Another is that the White House found claims of corruption in Russia politically awkward at a time when they were trying to get along with the man