(19.10.2015) The email sent by Secretary of State Colin Powell to George W Bush ahead of Blair’s visit to the then US president’s ranch in Crawford, Texas, falls squarely into this category.

Huge mystery has always surrounded this Crawford visit, which took place 11 months before the outbreak of war the following year.

Nobody knows exactly what was discussed between Blair and Bush. Most unusually for a summit meeting, the two world leaders were left alone together for long periods of time with no officials present to advise them or to take notes.