Until last week, when two fibre-optic cables were severed in the Baltic Sea, few people realised how vulnerable the UK is to internet sabotage. Suspicion over the most recent incident has fallen on a Chinese ship, the Yi Peng 3, which sailed over both cables - linking Finland to Germany and Sweden to Lithuania - around the time they were cut. Fortunately the disruption was minimal. But we are an island - and if our digital lifelines to the rest of the world were severed, Britain might not be able to survive. Here, we imagine how the country could be brought to total collapse within just two terrifying days.