The UK's power grid is relatively "vulnerable", an expert has said, after a major power outage in Spain and Portugal. Much of the two countries was brought to a standstill yesterday after a blackout switched off traffic lights and left people unable to access cash machines and telephone networks. Thousands have also been left stranded after transport networks were crippled. Spanish power distributors said this morning that more than 99% of power has been recovered.

Analytics director at energy group Montel, Jean-Paul Harreman, has now said that, while the outage was an “unprecedented event in modern energy markets”, it is “not particularly surprising”. This is because “countries that are on the edge of, and more isolated from the synchronous European grid tend to more easily see grid frequency deviations”. Mr Harreman added: “In island systems like GB [Great Britain] and Ireland, or peninsular systems like Italy and Spain, the AC synchronous interconnectivity with other countries is much lower, leading to a more vulnerable grid as flexibility and resilience has to mostly come from the inside."

The expert also noted that, by contrast, countries such as Germany are “surrounded by many other countries and connected with AC connections, in which assets operate that provide resilience to the grid frequency”, which needs to be kept at 50 Hz at all times to prevent blackout.

Mr Harreman added: “Whenever there is a deviation due to a power plant outage… there is sufficient flexible capacity to ‘catch’ the frequency before it goes ‘out of bounds'. This buys time to bring up other generation capacity to fill the gaps or take other measures.”

There had been rumours that the incident could have been caused by a cyber attack, but the European Commission's first vice-president and commissioner for competition, Teresa Ribera, has told media that there is nothing to affirm that what is behind the blackout was a boycott or cyber-attack or "anything intentional".

The Home Secretary, Yvette Cooper, said this morning that the UK has been looking at how to deal with “different kinds of challenges and threats” after the power outage.

Asked whether the power cut there had triggered a fear that British infrastructure could be affected in the same way, Yvette Cooper told Sky News that the UK has a “continued approach” to “resilience” and “security issues”.

She added: “We’ve been looking, as part of wider security reviews across the country, how we deal with both resilience and also different kinds of challenges and threats.

“Some of which can be the traditional security challenges, some of which can be the kinds of resilience – things that we’re talking about in Spain and Portugal – and we obviously support them and the governments there in the work that they’re doing.”