The UK’s nuclear submarines are vulnerable to a “catastrophic” cyber-attack that could potentially spark a nuclear war, a think tank has warned.

The report, titled “Hacking UK Trident: A Growing Threat” and published by the British American Security Information Council (Basic), said such an attack could “neutralise operations, lead to loss of life, defeat or perhaps even the catastrophic exchange of nuclear warheads (directly or indirectly)”.

The Ministry of Defence claims Britain’s four nuclear Trident submarines cannot be hacked while at sea because they are not connected to the internet – a claim the report authors said was “false and complacent”.

“Submarines on patrol are clearly air-gapped, not being connected to the internet or other networks, except when receiving (very simple) data from outside”, they wrote. “As a consequence, it has sometimes been claimed by officials that Trident is safe from hacking. But this is patently false and complacent.”

Malicious software could be secretly installed on the submarines’ computer systems when they are docked in the UK.

“Trident’s sensitive cyber systems are not connected to the internet or any other civilian network," says the report.

“Nevertheless, the vessel, missiles, warheads and all the various support systems rely on networked computers, devices and software, and each of these have to be designed and programmed. All of them incorporate unique data and must be regularly upgraded, reconfigured and patched.”

A Day That Shook The World: First nuclear submarine launched Show all 5 1 /5 A Day That Shook The World: First nuclear submarine launched A Day That Shook The World: First nuclear submarine launched 21st January 1954: The Nautilus, the world's first atomic submarine beginning her trials at Groton, Connecticut. Getty Images A Day That Shook The World: First nuclear submarine launched USS Nautilus, the world's first atomic powered submarine being launched at Groton in Connecticut. Getty Images A Day That Shook The World: First nuclear submarine launched Officers of the World's first nuclear powered vessel, the submarine USS Nautilus, stand to attention as Chief of Naval Operations Admiral Robert B Carney comes on board. Getty Images A Day That Shook The World: First nuclear submarine launched Admiral Robert B Carney observing the depth gauges of the world's first nuclear powered submarine 'Nautilus'. Getty Images A Day That Shook The World: First nuclear submarine launched A submariner puts a nickel in the jukebox on board the submarine USS Nautilus, the World's first nuclear powered vessel. The money will go toward the submarine's recreation fund. Getty Images

The replacement of the Trident submarines is a controversial political issue. Both Labour and the Conservatives have pledged to go ahead with the renewal, but Jeremy Corbyn has repeatedly spoken of his opposition to Trident and his belief in nuclear disarmament.

A cyber-attack on the NHS last month caused widespread disruption across the health service. The hack, designed to extort money from computer users, led to GPs and hospitals cancelling appointments and medical staff forced to use pen and paper for records after systems failed.

Michael Fallon, the Defence Secretary, has refused to deny that the UK's nuclear submarines use the same Windows XP software that was hacked in the attack on the NHS.