One of the main criticisms about Unlawful Killing is that it has been 100% funded by Mohamed Al Fayed. He's sunk somewhere between 2.5 and 4 million pounds into the documentary, depending upon which source you read.
Mohamed Al Fayed (pictured) has a personal stake in this story. It was his son Dodi who was in the car with Princess Diana. The couple were dating; and there has been persistent speculation that the Princess of Wales was pregnant with Dodi's child.
Since 1997, Mr Al Fayed has been convinced that his son and the princess were murdered. He has openly stated that Prince Philip, Duke of Edinburgh, was implicated.
Unlawful Killing certainly follows his version of events, but backs up its claims along every step of the way.
Keith Allen is unsympathetic to those who would dismiss the evidence, simply because of who funded its research and dissemination. He pointed out that most Hollywood films are funded by the Mafia, but no-one ever thinks that's significant.
But is it a conspiracy film? Let me be honest here and tell you that I have little patience with the term. 'Conspiracy' anything is the kind of stop word bandied about by people who don't want any challenges to the mainstream view.
Call anything a 'conspiracy movie' and you have effectively told the audience not to believe a word in it.
That is a point of view and, as an academic, I prefer my opinions to be based on solid evidence and rational extrapolation.
Unlawful Killing does suggest that there was a conspiracy. It points out the major players and those who would benefit from Diana's death. So yes, in the strictest sense, it is a film about a conspiracy; and there are unsettling conclusions to be reached.
However, I felt that it muddied the waters somewhat. For example, we are told at length about Prince Philip's family connections in the Third Reich - one brother-in-law was a high-ranking official in the Nazi party; another was a Stormtrooper. While sensational, I struggled with the relevance to the debate at hand.
Also the commentators equally could benefit from publicity here. One of the most ubiquitous speakers (and publicist for the film) is Noel Botham. As erudite an investigative journalist as he may be, it should be noted that he is also the author of a book claiming that Princess Diana was murdered.
Another familiar face was Kitty Kelley. As one of the closest friends of the Princess of Wales, she does have valuable insider information to impart. However, she also wrote a popular biography of the princess.
Unlawful Killing, to my mind, should be an important new element in the overall discussion, but there needs to be much more objectivity before it could be considered the final word.