When trip-hop doomsayers Portishead returned after an 11-year break in 2008, their album, Third, was an LP partly wedded to elements of Wiccan folklore. Less surprisingly, it was also full of the kind of sonic darkness prone to making the band themselves feel as uneasy as their listeners.

Adrian Utley, a multi-instrumental member of the trio chiefly known for his contributions as a guitarist and songwriter, was on bleaker form than ever. And given his band'’s tendency to issue records which are as sporadic as they are brilliant, Utley’'s new composition -– a piece of music as part of the National Trust'’s Great British Walk initiative - –is a cause for some anticipation.

Utley, you imagine, is a man who would enjoy a wintery stroll through Croft Castle, the Herefordshire manor house and complex his recording is intended to soundtrack a wander around.

Battles were once waged nearby, and hillforts and churches still stand within the grounds, including the tomb of Sir Richard Croft, a physician to successive monarchs during the 15th century.

But it’'s probably best known for its ancient Spanish chestnut trees –– Utley has used The Sonic Journey to carve a route through the tree-dominated landscape in a 15-minute walk visitors can download or receive in mp3 format at the castle, illustrated by a map he has drawn by hand.

"Adrian's music really captures the spirit of this special place,"” says Brian Muelaner, the Ancient Tree Advisor for the National Trust. “"Walking is the perfect way to get outdoors and explore the exquisite British countryside, particularly at this time of year with trees in wonderful colours of autumn.

"“They have inspired generations of artists. There is something remarkable about the power and beauty of ancient trees.”"

• Download the map and track from www.sonicjourneys.co.uk. Visit www.thespace.org to watch Portishead film-maker John Minton’s video based on The Sonic Journey.
  

• The Great British Walk, featuring hundreds of free downloadable walks and thousands of events across the country can be explored at www.nationaltrust.org.uk/greatbritishwalk