When it was dark

I had to borrow a copy of this book from a public library in the City of London, and it was a few years ago - so this from a fallible memory. The book is a curious and anti-semitic story of a great (Jewish) conspiracy to convince the (western) world that Jesus Christ's resurrection was a fraud. Everyone believes this, and as a result civilization falls wholly to pieces: murder and every lesser crime become commonplace. The hero proves that this is indeed a consipracy, unmasks the villain, and civilization immediately puts itself back together again. The book sold huge numbers of copies so it is curious how difficult it is to find an original print copy. Claud Cockburn, in his book "Bestseller", devotes a chapter to this work. Again from memory, Field Marshall Montgomery said that it was the one book that influenced him most in his life. And this was a work written by the Dan Browne of the first decade of the twentieth century (though the grammar was better), though obviously for anti-catholicism now read anti-semitism then.