The reason that Greenland could withdraw from the EEC is that it is an autonomous country within the Danish Kingdom. The City of London is a subsidiary jurisdiction within England, just as any city within the country. As a result it cannot make independent political arrangements with outside powers.
City of London Governance
The City of London is a city and county within London. It constituted
most of London from its settlement by the Romans in the 1st century AD
to the Middle Ages, but the agglomeration has since grown far beyond
the City's borders. The City is now only a tiny part of the
metropolis of London, though it remains a notable part of central
London. It is one of two districts of London to hold city status; the
other is the adjacent City of Westminster.
The City has a unique political status, a legacy of its uninterrupted
integrity as a corporate city since the Anglo-Saxon period and its
singular relationship with the Crown. Historically its system of
government was not unusual, but it was not reformed by the Municipal
Reform Act 1835 and little changed by later reforms.
It is administered by the City of London Corporation, headed by the
Lord Mayor of London (not the same as the more recent Mayor of
London), which is responsible for a number of functions and has
interests in land beyond the City's boundaries. Unlike other English
local authorities, the Corporation has two council bodies: the (now
largely ceremonial) Court of Aldermen and the Court of Common Council.
The Court of Aldermen represents the wards, with each ward
(irrespective of size) returning one Alderman. The chief executive of
the Corporation holds the ancient office of Town Clerk of London.
The City is a ceremonial county which has a Commission of Lieutenancy
headed by the Lord Mayor instead of a Lord-Lieutenant and has two
Sheriffs instead of a High Sheriff (see list of Sheriffs of London),
quasi-judicial offices appointed by the Livery Companies, an ancient
political system based on the representation and protection of trades
(Guilds). Senior members of the Livery Companies are known as
Liverymen and form the Common Hall, which chooses the Lord Mayor, the
Sheriffs and certain other officers.
Denmark is a sovereign state that comprises Denmark proper and two autonomous constituent countries in the North Atlantic Ocean: the Faroe Islands and Greenland.
Grønland [ˈɡ̊ʁɶnˌlanˀ]) is an autonomous country within the Danish
Realm, located between the Arctic and Atlantic Oceans, east of the
Canadian Arctic Archipelago. Though physiographically a part of the
continent of North America, Greenland has been politically and
culturally associated with Europe (specifically Norway and Denmark,
the colonial powers, as well as the nearby island of Iceland) for more
than a millennium. In 2008, the people of Greenland passed a
referendum supporting greater autonomy; 75% of votes cast were in
In 1985, Greenland left the European Economic Community (EEC), unlike
Denmark, which remains a member. The EEC later became the European
Union (EU, it was renamed and expanded in scope in 1992). Greenland
retains some ties with the EU via Denmark. However, EU law largely
does not apply to Greenland except in the area of trade.