It was the strike-hit era of Margaret Thatcher's government, and an industrial dispute threatened to completely halt vital plans to launch the Thames Flood Barrier.

A Teesside Docks dispute in 1982 meant the gates needed to complete the world's second largest moveable flood barrier could not be delivered to London.

Ministers feared a flood the following January or February, which would be "the most damaging natural disaster liable to affect these islands."

It launched plans to prevent what it feared could be a catastrophic tidal surge which could lead to hundreds of casualties and deaths, polluted water, electricity failure, structural damage, as well as a risk of looting and other outbreaks of civil disorder.

Parts of London, it feared. would be virtually uninhabitable, with mass evacuation needed.

Its plans included involving the unions to end the dispute, and pressing the GLC (Greater London Council) to work with the government.

However, if negotiations failed, a potentially deadly option was mooted, which meant blowing up parts of Kent and Essex to save Londoners.

A confidential Department of the Environment document from the time - released from the National Archives - suggests an option to flood low-lying land in Essex and Kent.

The document reads: "If all else fails it might be necessary to provide that, if a major surge of water was threatened, the flood defences downstream would be breached so that some of the water would flood low-lying land in Essex and Kent rather than central London."

The approach seemed "unlikely to prove practicable", it said.

It would involve the destruction of large section of defences, costing £250 million.

Explosive charges would have to be laid in advance, so they could be detonated when a tidal surge sufficient to flood London seriously was on its way.

This was roughly when it hit Southend, the report said.

But the height of the tidal wave couldn't be predicted accurately, so defences could well be blown up "unnecessarily" - potentially costing lives in Kent and Essex for no reason.

The report says: "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."

The government would need to explore two aspects particularly if the option was to be considered:

• One was how much warning should be given to those in low-lying areas of Essex and Kent before the defences were breached
• The other was that the defences didn't belong to the government - but to the water authorities.

In the most chilling part of the document, the report says: "It seems very probable that insufficient time would be allowed for evacuation and there would thus be a major risk of loss of life".

"It seems very probable that insufficient time would be allowed for evacuation and there would thus be a major risk of loss of life" - government report from 1982

The confidential report claims the option to breach the downstream walls was "doubtful".

If it was considered sensible to explore it further "it would need not only very thorough investigation but also sensitive handling because of the alarm which might be created in Canvey Island and elsewhere".

The report concluded the main priority was to bring pressure to bear on the strikers through the trade union movement.

In the end, the dispute was resolved and the Thames Flood Barrier completed - without loss of life to those families living in Kent's low-lying areas.