Under certain circumstances, where the activity is one of social importance, it may be justifiable to take even a substantial risk.
Watt v Hertfordshire CC  2 All ER 368, CA
A fire brigade was notified of a serious road accident: a person was trapped and heavy lifting equipment was urgently required. The lorry which usually carried the equipment was engaged in other work at the time, and the fire officer ordered the equipment be loaded into the back of an ordinary lorry. On the way to the incident, the equipment slipped and a fireman was injured. He sued his employers, and failed. Denning LJ said one must balance the risk against the end to be achieved. The saving of life or limb justified the taking of considerable risks, and in cases of emergency the standard of care demanded is adjusted accordingly.
Wooldridge v Sumner  2 All ER 978, CA
A press photographer working in the arena at a horse show was severely injured when he tripped while trying to get out of the way of D's horse as it tried to take a corner too fast. He sued for negligence, but the Court of Appeal said competitors in top-class sports events were expected to concentrate on maximising their performance. A mere error of judgement was not in itself enough to show a breach of duty.
Marshall v Osmond  2 All ER 225, CA
An escaping criminal was injured when the following police car crashed into his. The Court of Appeal did not directly invoke public policy, nor the maxim ex turpi causa non oritur actio, but emphasised instead the standard of care. The duty owed by a police driver, said Sir John Donaldson MR, was the same as that owed by any other, namely, to exercise such care and skill as was reasonable in all the circumstances. But where those circumstances were that he was driving alongside another car in order to make an arrest, the error of judgement he made in the instant case did not amount to negligence.
Rigby v Chief Constable of Northamptonshire  2 All ER 985, Taylor J
The police used CS gas to disable an intruder barricaded in a shop without first ensuring that firefighting equipment was available, and thereby caused a fire that seriously damaged the premises. The owner sued the police for negligence, and the judge said the defence of necessity is not available when the relevant circumstances are the result of D's own negligence in the first place. Even bearing in mind the pressures and burdens on the police officers in the situation with which they were dealing, they had a duty of care to the shop owner and they were in breach of that duty.