Wakehurst Place is a stately house set in majestic grounds; the rural offshoot of Kew Botanic Gardens, London. On a working day in summer, pensioners drift through the shade of exotic trees, sniff scented blooms, sip tea, gaze out over bucolic bliss.

‘Minus 20 degrees,’ says Michael Way, Head of Collecting at Kew’s Millennium Seed Bank Project at Wakehurst. He’s indicating heavy doors off an airlocked dry-room sunk deep into the ground beneath a gigantic modernist shed. Here are preserved seed samples of some 26,000 plant species from around the world, many of them endangered.