I know that's a pretty grand claim of mine in the title, but I really believe this is one of the most intelligent, well-acted, and chillingly effective films we've ever made. Made at the height of concern about nuclear warfare (this was the era of the CND Aldermaston marches), it takes the idea that by detonating two massive nuclear bombs at once we have caused the Earth to shift off its axis and ... gulp, we are now heading towards the sun! Much of the unfolding terror is seen through the eyes of journalists in a newspaper office covering daily what could be the oncoming end of the world. These scenes are highly effective indeed, most particularly the briefings in the Editor's office, and Leo McKern is splendid as a jaundiced hack getting his biggest (and most unwelcome!) story. As the days click on and society begins to unravel, with water rationing causing riots and old diseases making a comeback, you even get reminded of later terrifying docu-dramas like "The War Game" and "Threads". On a lighter note look out for a before-he-was-famous Michael Caine appearing briefly in one scene as a policeman doing traffic duty.