They entered through Russell Square station. For 10 minutes, the four of them sprinted along the tracks of the Piccadilly line towards a disused tunnel at Holborn. Their prize: a sight of one of the great trophies of London's urban exploration scene – the abandoned platforms of Aldwych tube station.
The expedition last year was supposed to be the second last stop in a tour of the capital's 18 "ghost" tube stations. Instead it has sparked a legal battle over the human rights of a community of photographers dedicated to visually documenting restricted areas across the world – and pointing out security loopholes.
To avoid a regular tube service, the explorers chose Easter Monday – four days before the wedding of Prince William and Kate Middleton. Above ground, one of the biggest security operations in the history of the Metropolitan police was swinging into action at an estimated cost of £20m. Officers searched lampposts and traffic lights for hidden bombs; 35 sniffer dogs scoured for traces of explosives; armed commandos trained to counter gun attacks and squads of police monitored the internet for potential plots.
And below the city, four members of the London Consolidation Crew exploration collective were running on the tracks. Their expedition was between 2am and 3am, when only maintenance trains are in use. But as one explorer, Otter, wrote on his website,
Silent UK: "At any moment the track on which we stood could have gone live, its guest of honour a 40mph mass of iron and steel singing our last goodbyes."
From Holborn they noticed the rails turn rusty and saw piles of flyers collecting at the tunnel's edges. And then, like hikers who'd reached the best view from the mountain, they saw the forest-green tiles of the platform edge.
For the next four hours they photographed the ticket halls, deserted walkways and antique lift system. Like their other trips – to the roof of St Paul's cathedral, the London Olympic Stadium, Battersea power station – they were careful to leave things as they found them; graffiti is taboo for urban explorers. When the battery on their camera went flat, they got ready to leave. They were interrupted by a shout: "Get on the ground!"
CCTV operators had alerted British transport police, who had issued a terror alert. After infiltrating 200 sites across the city over 10 years and getting away with it, they were busted.
"Normally we would have been dished off to the graffiti squad," Otter says. "But because of the wedding we ended up with detectives much higher up."
The explorers were put in cells and interviewed. Their laptops, cameras and hard drives were confiscated. Otter says: "The police pretty quickly realised our intentions and let us go with a caution."
Three months later an unassociated group of explorers was arrested after accidently derailing a small electric train on a one-off joyride on London's mail rail, a 23-mile underground network that carried post until 2003. The incident sparked an ongoing court case alleging damage to government property and aggravating vehicle taking.
