David Mamet, before his recent move from chilly Vermont to the warmth of Santa Monica, had a wood burning stove in his, an Edwardian roll-top desk and a bowie knife for hurling at the walls in periods of frustration. The shed at the bottom of the garden has long been the retreat of writers who wish to put a distance between the drowsy warmth of home and the chill of the "word factory".

I, too, have my retreat, an old beaten potting shed, that sits in the bottom right corner of the garden, 49 strides down a pebble path strewn with bluebells, past the white blossom of the cherry tree and the thin branches of its neighbour, the apple. Inside, to the left, is a pile of bags, and boots and a Black and Decker leaf blower. A brown suitcase patiently gathers mould on top of a wooden chest, while two tall brown candle-sticks stand by in case they are required for illumination. The two shelves that line the wall bear books from projects past – histories of Cuba; Winston Churchill's six-volume history of the Second World War; the daily testimony of a tragedy; as well as boxes of micro-tapes, 15 years of audio interviews. The desk is a cherry wood hulk from Office World, stained by raindrops from the leaking roof, spiders' webs and the bodies of beasties.

There is no heating or electricity. My nostalgic desire for a paraffin lamp like Paladin from Glen Michael's Cavalcade bowed out in the light of my clumsiness and the serious threat of immolation. So, instead, a Coleman chargeable lamp illuminates the room on dark nights. In winter I wear jeans and a fleece, knitted bunnet, dressing gown, fingerless mitts and an old blue throw decorated with red roses. I bought an hourglass to focus my mind, but the cold does a better job. Japanese classrooms were once unheated for a similar reason.

There is a joy in disconnecting from the electrical current of daily life, in stepping off the grid and exchanging laptop for pencil and paper. The silence, however, is brief as birdsong enfolds the shed, while the scrapping and scrambling on the roof above my head heralds the arrival of the squirrel, who, a few seconds later, will charge purposefully along the stone wall, inches from my dirt-smeared and cob-webbed cradled window. One winter's night I looked up and into the eyes of a fox, peering in from the darkness, inquisitive about the lighted room behind the glass pane. As I write, a squirrel has just bulleted by.

On a thin shelf, six inches above the desk, sits a battery powered radio I have never switched on, a worn white rock from the blue waters of Barbados and an old Christmas card which bears a photograph of a fir tree lighted with candles, standing in the centre of a broken dilapidated shed. The roof has been torn off and opens on to a pale blue sky. Glassless window frames have dark trees beyond. The card bears a quote from Graham Greene, which, with this particular column now finished in pencil, and with the schlep into the office ahead, I ponder the lines as I retrace my 49 steps: "Behind the complicated details of the world stand the simplicities."