The next battle of Britain will be fought under the sea – if we lose, the consequences will be disastrous

As Keir Starmer announces the government will buy 12 new nuclear fighter jets, there is a far more urgent threat to our security – and it could lead to food shortages and blackouts very quickly, says defence expert Francis Tusa

Imagine the scenario. You wake up and there is no power in your home. You can’t turn on the lights or television, the freezer is defrosting, and there is no way to cook anything. The wifi is down, phone networks have ceased to operate, and cash machines don’t function. The shops are shut, there is no power for the railways and airports, and hospitals are running on backup generators – but for how long, nobody knows.

The threat of this happening is no longer imaginary; it is being discussed at the highest levels. At recent conferences (all under the Chatham House Rule), speakers have noted that the loss of data transmission could cause UK supply chains across much of the economy to crash – leading to food shortages and widespread civil unrest. It has been firmly stated: this is no longer a hypothetical threat. An attack on critical infrastructure is not a question of if, but when.

As it is announced that the UK is set to buy a fleet of new fighter jets capable of carrying nuclear weapons, many saw this as a huge win for the Royal Air Force. But others are arguing that we need to pay just as much attention to what’s happening under our seas as we do in our skies.

At its peak, the UK imports up to 15-20 per cent of its electricity from Europe – all of it carried by undersea cables. There are four main European gas pipelines, and 75 per cent of UK gas arrives via undersea routes. More than 60 undersea cables carry internet traffic, telephony, and other data – more than 95 per cent of data/internet flows travel beneath the sea’s surface.

Damage to or destruction of any of these pipelines or cables could have a serious impact on the UK. Protecting them must become a national priority, because this is where a direct attack on our nation is most likely to happen.

The vulnerability of undersea infrastructure is increasingly exposed, and the threat is being raised more frequently. Nord Stream 2, data cables between Finland and Estonia, and internet cables near Taiwan have all sustained damage in attacks in recent years. Some of these incidents can be attributed to known actors – Taiwan’s cable damage, for example, was reportedly caused by a cargo vessel linked to China reported to be dragging its anchor in the precise area of the cables. Other attacks remain unattributed, though there are strong suspicions – such as the Estonian incident being linked to Russia.

The 2025 National Security Strategy, published yesterday, warned: “Critical national infrastructure – including undersea cables, energy pipelines, transportation and logistics hubs – will continue to be a target.” It also provided a staggering estimate: “The cost to repair a single damaged fibre optic cable is up to £1m, and £100m for power cables per incident.”

It now must be assumed that a hostile actor – Russia being the most likely in the case of the UK – will seek to exploit the vulnerabilities of undersea cables during periods of heightened tension, with the aim of at least disrupting, if not crippling, the UK and Europe. In the transition to any conflict, it is highly likely that attacks on connecting cables would be carried out stealthily.

An operator works on an undersea fibre optic cable at Arrietara Beach in Spain (AFP/Getty)

Russia is believed to operate several dozen “intelligence ships” that can monitor or attack undersea cables. The Yantar, for example, spent several weeks earlier this year patrolling the Irish Sea, surveying cables between the UK and Ireland using unmanned underwater vehicles (UUVs). It’s also believed that Russian submarines have the capacity to launch similar UUVs capable of targeting undersea infrastructure.

So, what can the UK do to counter this growing undersea threat?

The 2021 Integrated Review announced that the Royal Navy/Royal Fleet Auxiliary would acquire a new type of ship: the multi-role ocean surveillance ship (MROSS), designed to protect critical undersea cables.

Briefings suggested that at least three ships would be procured. In 2021, an offshore support vessel was bought, renamed RFA Proteus, and converted at Cammell Laird in Birkenhead. It entered full service in 2023, though it has experienced maintenance issues that have limited its operations.

A second MROSS – possibly UK-built – was discussed, but this year’s strategic defence review gave no specific commitment to further vessels or new undersea capabilities, just some vague suggestions.

The Chinese ship Yi Peng 3 (right), being monitored by a Danish naval patrol vessel last November (Ritzau Scanpix/AFP/Getty)

While Starmer has signalled his intention to create a hybrid Royal Navy using AI and forming a new digital warfighter group, many are concerned that the new systems needed to counter the threat to underwater infrastructure won’t arrive until the early 2030s. The 2025 review also suggested the Royal Navy may contract certain (unspecified) capabilities to commercial partners.

Operating non-combat surveillance ships is one such option. Procuring a fleet of our own unmanned underwater vehicles to protect critical infrastructure was another key suggestion – but again, no confirmed details. Fixed sonar systems, common in the North Atlantic during the Cold War, are being considered again, but plans remain unclear. If the consequences of an attack would be as serious as those being discussed, defensive preparations feel far too vague and slow.

The problem is evident. Despite the rising threat, investing in undersea defence has become less politically and financially appealing than purchasing warships. Using a £500m-plus frigate to patrol oil or gas pipelines is still being seen as wasteful. In times of tight budgets, defence services often prioritise combat ships over support systems that don’t directly contribute to warfighting.

The sun sets over the Manhattan skyline during a major power cut in 2003 (Getty)

In a febrile “war-footing” atmosphere, it’s understandable that UK defence has many urgent and costly needs. But the threat of an attack on an electricity interconnector or a gas pipeline should not be underestimated. This would have grave consequences for the UK. We not only need increased surveillance of undersea infrastructure – we must also build the capability to repair and recover it quickly, should the worst happen.

We need only look to the Finland-Estonia cable, which remained offline for more than six months – even though its repair was made “easier” by the relatively shallow waters (their maximum depth is around 100 metres). The North Sea (up to 700 metres), and the Atlantic (with an average depth of 3,000 metres), would pose far greater challenges.

Does the UK have the capability to rapidly repair or replace a damaged cable or pipeline? Possibly. But with no real urgency in getting our underwater defences up to speed, all bets are off as to how the country would really cope with an undersea crisis.