What is the test for damages for injuries sustained by a police officer who intervened to stop a runaway horse in a busy street?

In Haynes v. Harwood & Son, supra, the plaintiff, a police constable, was on duty inside a police station in a street in which, at the material time, were a large number of people, including children. Seeing the defendants’ runaway horses with a van attached coming down the street he rushed out and eventually stopped them, sustaining injuries in consequence, in respect of which he claimed damages. It was held (1) that on the evidence the defendants’ servant was guilty of negligence in leaving the horses unattended in a busy street; (2) that as the defendants must or ought to have contemplated that some one might attempt to stop the horses in an endeavour to prevent injury to life and limb, and as the police were under a general duty to intervene to protect life and property, the act of and injuries to the plaintiff were the natural consequences of the defendant’s negligence.