Middlesex Guildhall (now the Supreme Court), Westminster.
It is still very common to see places in outer west and northwest London described as being in the non-existent county of Middlesex, as in Greenford, Twickenham, Wembley, etc. In fact the county was abolished in 1965, and only lingered on as a postal address until 1996 when postcodes replaced the need for county names. As many places are no longer in counties, these old names have become superfluous and unnecessary in postal addresses.
Middlesex, being so close to the capital, always had many strange anomalies. Due to boundary changes in the 19th Century the whole southeast of the county, which included the location of the Guildhall and many other administrative centers, were transferred to the London County Council. Prior to that Middlesex bordered the tiny square mile of the ancient City of London.