PERHAPS IT’S Thomas Hardy’s greatest poem, and he didn’t even write it – at least not with a pen – as my son and I found out when, with an hour to kill before catching a train home, we went for a wander behind St Pancras Station. After a weekend in the concrete and blare of the city, seeing what looked like a scrap of ancient woodland we pushed eagerly through some iron gates. It turned out to be the graveyard of St Pancras Old Church, one of the oldest centres of Christian worship in southern England. Fed on the alluvial mud of the submerged River Fleet, and the centuries of bones, the towering plane trees turn this corner of London into a rainforest. One tree was smaller than these giants, however, and sealed off behind a hedge and a wicket gate. We approac