In Edwards v National Coal Board [1949] 1 All ER 743 CA, the Court of Appeal held that 'reasonably practicable' is a narrower term than 'physically possible' and implies a computation between quantum of risk on the one hand and the time, cost and trouble of safeguards on the other. If a defendant can show a gross disproportion between them, the risk being insignificant in relation to the sacrifice, the duty holder discharges the onus that is upon him or her.
In Mersey Docks and Harbour Board Ltd v Coggins and Griffith (Liverpool) Ltd [1946] 2 All ER 345 HL, the House of Lords held that where a crane was hired with a driver and that driver was negligent, the driver's employer would be vicariously liable. Where the negligence was in the way in which the hirer used the crane then the hirer would for that purpose be the employer of the driver. The terms of the contract between the hirer and the employer cannot affect liability to the injured person.