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1 August 2013, 12:21 | Updated: 1 August 2013, 12:28
It has emerged that Government officials thought of deliberately flooding Essex and Kent to try to stop central London from being swamped by a tidal surge.
According to newly-released secret papers, the plan was suggested because gates for the Thames Barrier were stranded by a dock strike in Teesside triggering fears that London would be unprotected in a flood.
The idea was to breach flood defences downstream so that some of the water would flood in to low lying land in Kent and Essex, the contingency planning documents dating from July 25, 1979 to December 22, 1983 from the National Archives state.
Such drastic action would have meant "major political difficulty'' for the Government, it was stated.
The cost, the need for explosive charges to be laid in advance and the potential legal wrangles which could follow because the flood defences belonged to several water authorities were all problems. The document notes that either way it "needs thorough investigation'' and "sensitive handling'' but it is "doubtful whether this option should be contemplated''.
There was one chance in 50 of a tidal flood in London in any one season, according to a July 1981 Environment Department memo, but "almost total protection'' would be provided by the Thames Barrier which was due to be finished by December 1982.
A doom-laden image of a severe London flood as "the most damaging natural disaster liable to affect these islands'' is painted in the document.
There were fears of looting, civil disorder and "mass evacuation may be needed'' as large parts of the flood zone would be virtually uninhabitable.
The document states: "It is generally accepted that there would be casualties, resulting from such causes as collapse of buildings, open manholes in flooded roads and individual failure to heed warnings and that, depending on the severity of the flood, deaths could be numbered in the hundreds rather than dozens.''
Polluted stagnant water, flooded sewers, widespread electrical failure,damaged roads, bridges and buildings plus earth slippage and disrupted telephone and public transport network would all be on the cards.
The dock dispute had stopped the loading and shipment of the gates.
Work to ensure the barrier was built in time was re-arranged but still remained under threat as the last remaining four gates and other machinery was still being held up in Teesside with no guarantee of when they would be released.
In February 1982 Ken Livingstone, then the leader of the Greater London Council, wrote to the Transport, Environment and Employment Secretaries stressing the "urgency'' of the situation. He hoped the Government might be able to stop the strike and release the much-needed gates.
It was feared the situation would be worsened by the downstream bank-raising works which would effectively funnel surge tide in to central London.
The impact of a major flood in London would be "incalculable'' he said, noting that "significant financial incentives have been and will be paid to contractors'' in an effort to be ready for the the November 1982-83 flood season.
Urging the Government to "intervene constructively'' Mr Livingstone wrote: "Any initiative could prove valuable in achieving the urgent release of the barrier gates. It has been suggested that a relaxation of current financial constraints might possibly be helpful in resolving the overall dispute.''
Behind closed doors the Government had decided that it would resist any attempt by Mr Livingstone to put them rather than the strikers "on the spot'', the documents note.
Settlement talks were being held at Acas. It was also suggested that the army could be used to deliver the gates so they could be fitted by Thames Barrier workers.
A Home Affairs department paper later points out that flooding Kent and Essex "seems unlikely to prove practicable''.
Large sections of defences would have to be destroyed "which together have cost £250 million''.
Explosive charges would have to be laid in advance but there were doubts about when exactly to trigger them.
It was noted: "The last measurement of tidal surge is at Southend, approximately an hour before it would reach central London, but the height of the eventual tidal wave in central London could not be predicted with complete accuracy, and thus the defences could well be blown up unnecessarily.
"There is a major political difficulty in that the Government would have to take responsibility for deliberately flooding Kent and Essex in order to protect central London.
"It seems doubtful therefore whether the breaching of the downstream walls should be contemplated. If the committee decided that the possibility was worth considering, it would need not only very thorough investigation but also most sensitive handling because of the alarm which might be created in Canvey Island and elsewhere.''