How has the law of negligence evolved in the context of a personal injury appeal?

After a general discussion of the manner in which various principles in the law of negligence had evolved, Lord Diplock at p. 1061 said: "In the present appeal, too, the conduct of the defendant which is called in question differs from the kind of conduct discussed in Donoghue v. Stevenson in at least two special characteristics. First, the actual damage sustained by the plaintiff was the direct consequence of a tortious act done with conscious volition by a third party responsible in law for his own acts and this act was interposed between the act of the defendant complained of and the sustention of damage by the plaintiff. Secondly, there are two separate 'neighbour relationships' of the defendant involved, a relationship with the plaintiff and a relationship with the third party. These are capable of giving rise to conflicting duties of care. "This appeal, therefore, also raises the lawyer's question: 'Am I my brother's keeper?' A question which may also receive a restricted reply."