As a rising star of the English Bar, Mayne applied in 1829 to be one of the Joint Commissioners of the new Metropolitan Police and was selected without interview. His senior colleague was to be
Lieutenant-Colonel Charles Rowan. Rowan was to provide the discipline and organisational skills, while Mayne was to provide the legal expertise. They took up their new appointments on 7 July 1829 and were to become firm friends, working closely together until Rowan's retirement 21 years later. Later that month, they moved into their offices in 4
Whitehall Place and set about the monumental task of creating the new police force from nothing. On 29 August, they were sworn in as Justices of the Peace by
Lord Chief Baron Sir
William Alexander. On 16 September, the two Commissioners personally swore in their new constables at the
Foundling Hospital. The new force first took to the streets at 6:00 p.m. on 29 September. Mayne was responsible for the second section of the
General Instruction Book, which laid down the legal standing and powers of a police officer and the law he was required to enforce. These instructions are still the basis of the powers of a
British police constable and made it clear that police officers did (and do) not have
carte blanche to give orders to private citizens without a
warrant from a
magistrate. Private citizens could make complaints against police officers and pursue them in the courts if necessary. It was not a police officer's job to enforce his own morality or that of a particular section of society. Mayne was a more rigid and abrasive man than Rowan, and frequently clashed with
Samuel Philipps, the
Permanent Secretary of the
Home Office, who believed that the Commissioners should answer to him and his officials, and not just to the
Home Secretary. It was a mutual dislike, and although Rowan was more tactful, the Metropolitan Police and Home Office were at odds for sixty years. In 1848, Mayne was appointed
Companion of the Order of the Bath (CB). Since Rowan was at the same time appointed
Knight Commander of the Order of the Bath (KCB), there were suggestions in the press that Mayne may have been deliberately passed over (although in fact Rowan had held the CB for his military services since 1815 and was therefore simply being promoted in the order). ==First Joint Commissioner==