Imagine a million square kilometres of unrivalled ocean splendour. South Georgia and the South Sandwich Islands (SGSSI) are easily the most important wildlife haven under British jurisdiction – yet when we undertook this swim in November 2017, only 2% of the waters around these biodiversity hotspots were fully protected.

The purpose of this swim was to urge the British government to do better.

As the Amazon is to land, South Georgia and the South Sandwich are to oceans. The astonishing wildlife here includes Antarctic fur seals, southern elephant seals, myriad whale species and vast colonies of penguins. Its carbon sequestration potential and its role in combatting climate change cannot be understated. And since the islands do not support any local communities, there is simply no reason not to fully protect these precious waters from outside interference of any kind.

On November 7, 2017 Lewis pioneered a long-distance swim from King Edward Point, Grytviken, to the beach at the base of the disused whaling station, just a stone's throw away from the final resting place of Sir Ernest Shackleton. Lewis was watched over for the entire kilometre swim by a group of enormous elephant seals.

Just over a year later, after persistent pressure, the British government increased protection in SGSSI from 2% to 23% full protection. The recent announcement of a further 166,000km² – an area of water larger than England and Wales combined – will bring the level of protection to 36%. We see this as an achievement, but it is just a stepping stone: 77% of these waters remain unprotected. It is within the power of the United Kingdom – in fact we would argue that it is its duty – to unilaterally protect these precious waters, for the benefit of the entire world. We won't stop until we see this happen.