Allen, father of popstar Lily, is quoted as saying in The Independent: "To this day I absolutely believe that it wasn’t an accident. I just know."
The actor interviewed Harrods owner Mohamed Al Fayed, whose son Dodi was killed along with driver Henri Paul in the 1997 Paris crash, for a 2005 documentary and he told Allen: "All that happened to me was after the murder of my son and Diana. I challenge the b******* who did this to me, MI6, [to] say this is by order of the Royal Family."
Fayed has long believed that the car accident was engineered by British intelligence on the request of Prince Philip.
Friends of the late Princess have urged Fayed to end his conspiracy theory claims, with one telling the Daily Mail: "It has been over ten years and surely even he must acknowledge that we have had the most thorough of investigations."