Ring of steel (London)

The Traffic and Environmental Zone, commonly known as the "ring of steel" is the security and surveillance cordon consisting of road barriers, checkpoints and several hundred CCTV cameras surrounding the City of London, the financial district at the heart of Greater London. The measures have been used since the 1990s to deter terrorism and other threats.

According to a 2011 Freedom of Information Act request, the total number of local government operated CCTV cameras in the City of London was 649.

The number of surveillance cameras that are part of the TEZ is often wrongly quoted as 500,000. This figure relates to Greater London, which has an area of 1,572 square km compared with the 3 square km of the City of London that the ring of steel covers. Furthermore, it has been acknowledged for several years that the methodology behind this figure is flawed, but it has been widely quoted.

The figure of 500,000 comes from a study by Michael McCahill and Clive Norris of UrbanEye published in 2002. Based on a small sample in Putney High Street, McCahill and Norris extrapolate the number of surveillance cameras in Greater London to be 500,000 and in the United Kingdom to be 4.2 million. More reliable estimates put the total number of private and local government surveillance cameras in the whole of the United Kingdom at around 1.85 million in 2011.

The "Ring of Steel" measures were introduced by Owen Kelly, then the City of London Police commissioner, following the Provisional IRA bombing campaign in London in the 1980s and early 1990s including attacks within the City such as the 1992 Baltic Exchange and 1993 Bishopsgate attacks. The "Traffic and Environmental Zone" was officially established in 1993.

The term "Ring of Steel" was borrowed from an earlier stage of the Troubles when the centre of Belfast was fortified against attacks; this fortified perimeter was known as the "ring of steel".

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