More than a million Britons at risk of 'catastrophic' water supply failure over threat from hostile states

The national risk register, published in July, estimates there is a five to 25 per cent probability of water infrastructure failing in a major urban area.

Such an event could cut drinking water and wastewater services to more than one million people, potentially forcing evacuations and shutting schools and hospitals.

The disruption could take months to rectify, with the potential severity ranked alongside that of a major pandemic.

The increased threat has been blamed partly on the danger posed by hostile states, alongside ageing infrastructure and increasingly severe drought conditions.

Paul Netherton, the former police national lead for resilience, identified climate change and hostile state aggression as two of the forces behind the heightened risk.

He told The Times: "Climate change has meant the water system is increasingly vulnerable. We have seen how vulnerable this summer with the droughts.

"There are not enough pumping stations and treatment plants to cope with the strain on the system and those that we have are often in need of an upgrade."

The national risk register estimates there is a five to 25 per cent probability of water infrastructure failing in a major urban area

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Mr Netherton, now a risk and resilience consultant, warned Russia could seek to exploit existing public anger towards Britain's water companies.

He said: "What is the one utility that the UK is really fed up with at the moment? The answer is water. If a hostile state can disrupt a water company with a cyberattack or contaminating the supply, the public will blame the companies.

"Their objective is to destabilise the UK, damage the society and economy, and make the population lose faith in our institutions."

The warning comes as England battles severe drought conditions following its driest July on record.

Hosepipe bans currently affect 29 million people, while reservoirs are just 59.8 per cent full on average - nearly a fifth below the seasonal norm.

Parts of southeast England received 85 per cent less rainfall than usual during August.

The National Drought Group warned on August 27 that "drought conditions will continue to worsen" without prolonged rainfall.

River levels were also falling at half of all Environment Agency monitoring sites the following day.

The mounting concerns follow a series of major problems with Britain's water network.

South East Water left 20,000 properties in Tunbridge Wells without supply for a fortnight, while South West Water was fined a record £1.85million after a parasite contaminated drinking water in Brixham, Devon.

Alan Smith, a former employee of several water companies who now runs consultancy Water-People, said longstanding failures had "now really come to bite".

He said: "When I was in the industry it was sacrosanct not to take any risk at all on drinking water. That is now being taken and you're seeing it played out at South East Water and a number of other companies."

A Government spokesman said: "The National Risk Register is a planning tool and not a prediction of future events.

“Between the two editions, we have made improvements to the risk assessment, following closer working with water companies.

“The reasonable worst-case scenario used for planning is now based on a larger water plant serving a far larger population than previous editions.

"This allows the Government to plan for a more significant risk and prepare our response accordingly.

“A record £104billion is being invested across the country to rebuild our water network after years of underinvestment. We are confident about the security of supplies across the UK.”