Employers could be held vicariously liable for staff misbehaviour in a broader range of situations following the Supreme Court ruling in Mohamud v WM Morrison Supermarkets. There is no 'reasonable steps' defence against vicarious liability for torts. Employers should therefore check they have appropriate recruitment and training processes, management and supervision of staff in order to minimise the risks of violence at work, and should also check the terms of their insurance.

The Supreme Court endorsed the current test requiring there to be a sufficiently close connection between what the employee was employed to do (viewed broadly) and the behaviour for it to be fair and just to impose vicarious liability. However, it overturned the Court of Appeal's application of this test to the facts, ruling that the employer was liable when its sales assistant at a petrol station left the sales kiosk and violently attacked a customer on the forecourt. The employee's conduct arose from his position serving customers for his employer and the employer should be liable, notwithstanding that the employee's role did not encompass dealing with customers away from the kiosk or using any level of force.  This can be contrasted with previous cases of vicarious liability being imposed in relation to the acts of night club bouncers, where the fact that their duties might involve some use of force on customers was determinative.

The ruling suggests a more liberal application of the close connection test, and raises questions as to where exactly the boundary will lie. It suggests that employers may well be liable for the actions of employees towards customers where their duties include interacting with customers in some way, even if the employee engages in a wholly different nature of interaction from that envisaged. The same may apply where employees' roles involve interacting with colleagues; in contrast it may be possible to distinguish the case where an employee, whose duties do not include dealing with customers, assaults a customer.

Employers should also bear in mind that in some cases they may also be vicariously liable for the acts of individuals who are not their employees. Vicarious liability may apply where the individual carries on activities as an integral part of the employer's business activities and for its benefit, and where the assignment of activities to the individual created the risk of the behaviour occurring.

In Cox v Ministry of Justice the Supreme Court ruled that the prison service was vicariously liable for the negligence of a prisoner who had accidentally injured an employee while working in the prison kitchens. The prisoner worked as an integral part of the prison service's catering business and the risk of the accident was created by assigning those activities to him.