An investigation must be carried out promptly

The Acas Code emphasises that any investigation must be carried out without unreasonable delay to establish the facts before memories fade.

Whether or not a delay is unreasonable will depend on the particular facts of each case and the extent to which the delay prejudices the worker and undermines to possibility of a fair hearing (Royal Society for the Prevention of Cruelty to Animals v Crudden [1986] IRLR 83). Relevant factors are likely to include:

• whether a claimant has admitted any of the allegations;

• whether the key facts were properly investigated at an early stage of the investigation and findings of fact made before memories faded (Lim v Royal Wolverhampton Hospitals NHS Trust [2011] EWHC 2178);

• the extent to which the allegations rely on memory, as opposed to paper evidence; and

• whether the individuals the employee wants to call as witnesses still work for the employer.

Difficult issues can arise where the police become involved. An employer has a wide discretion to decide whether to press ahead with an investigation or to delay it pending a criminal prosecution (Secretary of State for Justice v Mansfield [2010] UKEAT 0539/09/2403). An employee in this situation will need to take legal advice as to the extent to which it is advisable to cooperate with the internal investigation, given the criminal proceedings.