Whilst the power of the police to release a person on bail prior to trial has existed for centuries, the power to release on bail a person suspected of but not charged with a criminal offence has been available to the police only since 1925. The power to attach conditions to pre-charge bail is of very recent origin, having been introduced for the first time in 2003 but rapidly expanded since then. Whilst imposing restrictions on the liberty of a person should, constitutionally, be reserved to the judiciary, the fact that it was originally conceived, in part at least, as a mechanism for enhancing liberty reduced the constitutional tension created by allowing members of the executive such powers. However, the changing role of arrest in the investigation of crime and the granting of extensive powers to the police to impose bail conditions means that the police now have the ability to place controls on people not charged with a criminal offence for extended periods of time. It is argued here that this is in breach of the right to liberty under Article 5 of the European Convention on Human Rights and, in practice, may also breach other Convention rights.