Donoghue v. Stevenson is maybe the most famous common law case ever (even though it wasn't under the common law, arising as it did out of Scotland, and wasn't really a case, being decided on the pleadings). It inspired the sub-plot in Strange Brew, in which Bob and Doug attempt to get a case of beer by pretending they found a mouse in their stubbie (this leads them to get a job at Elsinore Brewery, leading in turn to their defeat of a plot by Max von Sydow to take over the world through psychoactive substances in beer. Psychoactive substances in fried chicken was the plot in Undercover Brother.)
Miss Donoghue alleged that she found a snail in a bottle of ginger beer manufactured by the defendant. The House of Lords overruled a 19th century precedent holding that manufacturer liability for latent defects causing personal injury could only be brought in contract -- thereby screwing over ultimate consumers who rarely had direct contracts with manufacturers. The Pithlord does not dispute the justice of this result.
However, I have never been fond of Lord Atkin's attempt to generalize. He shows a marvelous sense of Biblical rhetoric, but demonstrates serious conceptual confusion of the kind one would expect from an American judge.
Rolling the tape  A.C. 562 at p. 580:
At present I content myself with pointing out that in English law there must be, and is, some general conception of relations giving rise to a duty of care, of which the particular cases found in the books are but instances. The liability for negligence, whether you style it such or treat it as in other systems as a species of "culpa," is no doubt based upon a general public sentiment of moral wrongdoing for which the offender must pay. But acts or omissions which any moral code would censure cannot in a practical world be treated so as to give a right to every person injured by them to demand relief. In this way rules of law arise which limit the range of complainants and the extent of their remedy. The rule that you are to love your neighbour becomes in law, you must not injure your neighbour; and the lawyer’s question, Who is my neighbour? receives a restricted reply. You must take reasonable care to avoid acts or omissions which you can reasonably foresee would be likely to injure your neighbour. Who, then, in law is my neighbour? The answer seems to be - persons who are so closely and directly affected by my act that I ought reasonably to have them in contemplation as being so affected when I am directing my mind to the acts or omissions which are called in question.
In this short passage, Lord Atkin distinguishes and then confuses both acts and omissions and moral and legal duties. He uses the term "injury," which sounds like harm-regardless-of-right, but brings to a lawyer's mind the phrase "damnum sine injuria ," which emphasizes that some interests are necessarily not legally protected. He presents the remarkable (and false) claim that there must be a general formula for liability in negligence as something he will at present content himself with. It is also wrong that the legal duty is always more limited than the moral one, since it is sometimes more extensive. As an attempt to make a general formula for negligence law, Lord Atkin's dictum is even worse than Anns.
So why does the passage resonate as much as it seems to? I think it is because of the interesting reversal of Christian theology. There is an overt reference to the tale of the Good Samaritan, and an implicit one to the contrast between law and grace in Romans. The relationship with Jesus's parable is interesting. Atkin invokes the universalism of Luke 10 in favour of an expansion of tort liability, while recognizing that as a coercive force, the law is always on the side of Pilate.
Photograph of snail from macrophile.
Update: The confusion between moral and legal duties arises in the definition of neighbours as "persons who are so closely and directly affected by my act that I ought reasonably to have them in contemplation..." "Ought" here either means a moral "ought" or a legal "ought". But if it is a moral "ought", then he has just confused moral and legal duties again. And if it is a legal "ought", the definition is circular.
The same sentence has him go back and forward between "affected by my act" with no mention of omission and "the acts or omissions which are called into question." It is surely correct that omissions can sometimes give rise to liability. It is surely wrong that they give rise to liability whenever acts would.