It is unlawful to treat employees less favourably because they are married or in a civil partnership. In common with other types of discrimination, this applies across the entire working relationship from the recruitment process; throughout employment and up to the provision of references post employment.
Initially, in interpreting the Equality Act 2010, Employment Tribunals considered that discrimination was established if a married employee was treated less favourably than an unmarried employee.
Thus in Dunn v Institute of Cemetery and Crematorium Management UKEAT/0531/10/DA , Mrs Dunn had her claim upheld because she had been treated less favourably as a result of her marriage to a man with whom the Chief Executive of the defendant company had an acrimonious relationship.
Subsequently, however, in the case of Hawkins v Atex Group Ltd  IRLR 807 a tribunal established the comparator against which discrimination could be judged. In this case an employee was dismissed because she had been employed by her husband in breach of an instruction that family members could not be employed. The case was dismissed because the tribunal considered that it was not the marriage at the root of the dismissal but the fact that they were in a close relationship. The tribunal in this case established that in order for married or civil partners to have been discriminated against they would have to be treated less favourably than others in a close relationship. So, if common law spouses are treated in the same way then discrimination is not established.
This case has a particular relevance for companies which have a policy of preventing married couples from working in the same department or within the immediate hierarchy. Such a policy is acceptable because it is the proximity of the relationship that is key and not the existence of a marriage or civil partnership.
Frequently it is single employees and common law couples who suffer discrimination. Many companies offer ‘death in service’ benefits to the spouses and civil partners of their employees, for example. Such benefits are less commonly available to cohabiting couples. Unfortunately because being in a ‘common law’ relationship is not a protected characteristic under the Equality Act 2010 then they have no right to make a claim for discrimination. This has likely come about because of the difficulty of establishing the longevity and permanence or otherwise of a common law partnership.