Dan Brown's book The Da Vinci Code may be a novel, but Brown claims that his book is based on research and that all the art, architecture and secret societies he describes are real.

It's a controversial claim because, if based in truth, The Da Vinci Code threatens to turn our view of history on its head. Millions of readers have been hooked, but what do historians think of the book and do its major claims stand up to scrutiny?

Has the truth about the Holy Grail been suppressed by the Catholic Church? Has the Grail been kept safe by powerful secret societies? And is the real truth about the Grail encoded into Leonardo's great painting of the Last Supper?

Tony Robinson sets out to discover the facts about the Holy Grail and cut through the thicket of mystery that surrounds the subject. Like many Grail hunters before him, has Dan Brown has been duped and could one of the most alluring elements of the modern Grail obsession be an elaborate hoax?