The line of trees beside the road into Tenbury Wells are bare of leaves at the beginning of December. But on their spindly branches are huge clumps of mistletoe, weighing them down like muffs on the skinny arms of dowagers. Most of the country’s mistletoe grows in a small area of England – Worcestershire, Herefordshire, Gloucestershire, the counties around the Malvern Hills – but no one is quite sure why; it may be the number of orchards (mistletoe grows well on apple trees) or the climate of cold winters and warm summers.