If Electricity is the blood system of a modern society, then communications is the nervous system. A research briefing produced by the UK Government's Parliamentary Office of Science and Technology (POST) provides an introduction to the structure and regulatory framework that the infrastructure works within, focusing on potential threats to reliability. At a brief four pages it's well worth reading and will briefly be summarised here with observations: interested readers are strongly encouraged to refer to the source document.
Accompanying the full report, the following key points are highlighted (text slightly edited, links to further reading added):
Further information on the risk of cyber attack is provided in another POST report "Cyber Security of UK Infrastructure".
The telecommunications network is of course highly dependent on a stable electricity supply. Even short power outages are liable to affect communications seriously as outlined in this page discussing problems which arise when electricity fails,based on practical experience caused by flooding in Lancaster.
Whilst fixed-line telephone links tend to have battery and/or generator backup, allowing houses with old-fashioned passive telephones to continue making and receiving calls during limited-duration disruption, this is nowadays very much 'old school' technology in the process of being retired. Internet and mobile telephony increasingly form the main media by which people receive information nowadays and both are either immediately or very quickly rendered inoperable during power failures. Longer term disruption will be likely to cause the loss of fixed-line telephony also when telephone exchange batteries run flat (some hours rather than some days). In the UK telecommunications providers have a legal obligation to provide access for their customers to emergency responders during power cuts (the document cited mentions providing this capability for one hour from the start of the power failure).
Should a widespread loss of telecommunications occur the results are liable to be extremely harmful. As the flooding in Lancaster showed, payment systems stop, ATMS cease to operate and access to cash or purchasing becomes impossible. Furthermore, as mentioned in the Cranfield Food Resilience report the distribution and reordering of food (and other) supplies is now highly automated and entirely dependent on electronic ordering systems with a fallback to paper-based ordering not only unrealistic but potentially needing emergency legislation to circumvent traceability and safety requirements.
As the POST report points out, vulnerabilities do exist in the telecommunications infrastructure but these are of reasonably manageable levels and not thought liable to sudden-onset prolonged failure. Short-term failures can be worked around, traffic re-routed and steps taken to keep reasonable levels of service maintained in circumstances except for disaster situations, in which case telecommunications becomes the victim rather than the instigator of the emergency.
In the case of an emergency situation arising, UK government has a published framework for dealing with the situation. Whether this would prove adequate in practice is unknown. There is, for example, provision in the emergency plan for making available radio frequencies to the military - but speaking from personal experience, considerable parts of the radio spectrum are already reserved to the military and I see no evidence that they have the equipment or training to do much useful with it in the scale of emergency that might require these kinds of powers.
The Policy Exchange report of 2017 makes for alarming reading. Key points and assertions include:
"It is a little known or appreciated fact that well over 95% of everything that moves on the global internet passes through a network of just 200 undersea fibre-optic cables; some as far below the surface as Everest is above it. It is not satellites in the sky, but pipes on the ocean floor that form the backbone of the world's economy. ... Were the network to disappear, the entire capacity of the earth's satellite network could handle just 7% of the communications currently sent via cable from the United States alone"
Supporting evidence for the above can be found in a report published in 2013 by the Asia-Pacific Economic Forum.
The UK telecommunications infrastructure is a crucial component of the economy and to lose it would instantly precipitate a major emergency.
There is no evidence of structural risk and whilst external threats exist, particularly in the cyber sphere and the vulnerability of cable connections, survival-level threats are hard to substantiate. There is no doubt that terrorist or state-level threats exist to external connectivity via cables but this in and of itself does not immediately create a life-threatening situation.
Until or unless unknown vulnerabilities in the system are exposed it appears likely that forseeable disruption to the system would be partial rather than total and there is a government response framework for dealing with such a situation (though how worked-through and tested is another matter).