The Former Middlesex Session(s) House or the Old Sessions House is a large building on Clerkenwell Green in the London Borough of Islington in London, England, formerly in the public sector as a courthouse but now used as a members' club for business networking.
It was built over the four years to either side of 1780, when it opened, for the Middlesex Quarter Sessions of the justices of the peace, replacing nearby Hicks Hall which had fallen into disrepair. Hicks Hall opened in 1611 had stepped into many of the lesser functions of the Old Bailey.
The Sessions House served as the most urban and senior magistrates centre and as a nascent administrative centre of Middlesex (which included Westminster and Islington for example) until county councils were created for Middlesex and London in 1889. This court and the old City and Liberty of Westminster Magistrates own 'Guildhall' (built 1805) were in the County of London. London County Council continued its use for magistrates in its area until sale in 1921 when remaining business was transferred to the Sessions House in Newington Causeway. Meanwhile, Middlesex administration saw a much-expanded burden of providing emergency services, a buildings and planning department, sanitation and road planning until its 1965 abolition, and so these functions took place in the former Magistrates' Guildhall as the Middlesex Guildhall which was rebuilt twice and has been finally reconfigured to revert to a judicial use: the Supreme Court of England and Wales.
From 1931 to 1973 the Old Sessions House served as the headquarters of Avery Weighing Machines, manufacturers of weighing-machines and scales. After their departure the building fell into further disrepair until in 1978 it was acquired and restored by a masonic trust and the following year opened as the London Masonic Centre, incorporating conference and social facilities.