My secret visit inside the hidden nuclear bunker hoarding digital gold – ‘the Fort Knox of Bitcoin’

self-destruct, corrupting everything inside – it’s our ultimate fail-safe,” Mr Parry said. Getting to this stage without an invitation is nigh on impossible. First, you have to contend with the outer fence and the guards, who are mostly ex-servicemen. I am shown around by a former Royal Marines Commando. He leads me through a blast door then a turnstile, down the stairs and through a series of dog-legged tunnels, past a sentry post and through a series of further doors and air locks. This leads us to the server room, which requires a regularly swapped fob and a key code for entry. Even then, after looking into a camera so that an off-site team can verify my identity, the servers are out of reach, visible only on a television screen in a tiny metal cupboard with room enough for about three people. “It’s about taking away the incentive for an intruder,” Mr Parry said. “Even if they get here, they have to think about getting out again.” Visitors’ backgrounds are checked before arrival and screened for links to the “dark web” – a hotbed of illegal activity. Every room in the bunker is encased in a “Faraday cage” to make it impervious to electromagnetic interference. Clients, who pay an annual fee of 0.36pc of their assets plus a set-up charge of several thousand pounds, are also covered by an insurance policy. The payout is linked to the value of the crypto assets as it was two hours before any theft and pegged to conventional currencies such as the dollar or pound. “In the past, successful heists elsewhere have caused a crash in the market,” Mr Parry explained. The policy also covers loss, he added. This year, around $200m of digital currency was lost after Gerald Cotten, the boss of crypto exchange Quadriga, died unexpectedly in India aged 30. As he was the only person with the key codes, his creditors and investors were unable to gain access to their funds.