Total loss of transatlantic telecommunications cables

This risk is featured in the full matrix, representing the averages of multiple different scenarios presented together in the ‘conventional attacks on infrastructure’ category.

Impact 5
risk indicator
ID 10
Risk theme State threats
Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


Transatlantic telecommunications cables are an underwater, fibre optic network of cables that run from one end of the Atlantic Ocean to the other. These transmit large volumes of data traffic that facilitate telephone communications and internet access. There is a risk that these cables could become damaged, which would disrupt communications across the UK and beyond. The system is generally resilient meaning there is a low likelihood of total loss of transatlantic telecommunications, but the risk would be impactful should it materialise.


The reasonable worst-case scenario assumes that transatlantic subsea fibre optic cables connecting the UK would be damaged over a number of hours, rendering them inoperable. The primary sector impacted would be communications. There would be considerable disruption to the internet, to essential services that rely upon offshore providers of data services (including financial services), and potentially to supply chain management and payment systems.

Key assumptions

The internet would begin to recover within hours as networks are reconfigured. Satellite communications would only provide a fraction of the bandwidth, and there would likely be an impact on European data networks.


A loss of a small number of cables could result from disruption at sea, such as a major underwater landslip across several hundred kilometres. The loss of connectivity would be more likely from damage to land-based infrastructure such as a cyber attack and could see cables connecting the UK being taken out of service, either directly or indirectly.

Response capability requirements

The required response would – at least temporarily – overwhelm the subsea cables’ sector and require an agreement with cable operators to prioritise cable repairs according to government or wider sector and social criticality needs. The government would at a minimum support coordination of the operation to restore connectivity through repair and mutual aid and assistance.


Repair would take a minimum of several months depending on the cause, location, availability of spare cables and specialist capabilities such as repair ships and specialist crews. The impact on the internet would begin to recover within hours as networks are reconfigured.