Can an employer prevent employees from political campaigning at the workplace in support of a particular political party?
Yes, if political campaigning (for example by distributing leaflets, or making speeches in support of a particular political party) causes disruption in the workplace, or causes intimidation or harassment of colleagues, employers can take action to prevent it. If the employee is carrying out campaigning during their working hours, instead of performing their work, the employer would be entitled to take disciplinary action. Employers should make clear to employees, preferably in a policy, that political campaigning should not take place during working hours, or on the employer's premises, and that employees should not engage in any activity that could create the impression that the organisation endorses a particular political party or view.
Employees cannot rely on their right to freedom of expression to avoid disciplinary action for disrupting the workplace. The right to free expression under the European Convention on Human Rights is not absolute and should be balanced against the rights of others. Employers have a duty to ensure that employees are not behaving in a way that amounts to harassment of their colleagues, and employees must not act in a way that breaches their contract with the employer.
It is unlikely that an employee could claim that being prevented from political campaigning is discrimination on grounds of their religion or belief. Support for a particular political party is unlikely to be a "belief" protected under the Equality Act 2010, but a belief based on a political philosophy could potentially be covered (Grainger plc v Nicholson  IRLR 4 EAT). However, even if an employee's political belief is found to be covered by the legislation, a claim for discrimination is likely to fail if the employer can show that the prohibition of political campaigning applies to all employees regardless of their political views, and that the reason is to avoid disruption to the workplace, or to prevent the intimidation or harassment of employees or customers.