To ask the Secretary of State for the Home Department what is the average length of time between the commission of a perjury and charges being brought by the CPS. 
The relevant information is not available. The decision whether to lay a charge of perjury, as of any other offence, is taken by the police in accordance with the Police and Criminal Evidence Act 1984, if they are satisfied that they have enough evidence to do so. The time taken will depend on a variety of factors, including the complexity of any case and the extent to which the necessary evidence is obtainable. In reaching that decision, the police may seek the advice of the Crown Prosecution Service as to whether a prosecution should be brought against a suspect.