True, but the thermal efficiency of charcoal is a lot lower than coal. Meaning that for a given amount of ore, the volume of charcoal you would need is even higher. You would need a lot of forestry to supply a lot of charcoal. The Forest of Dean springs to mind. Easy acccess via the Severn estuary.
Cornwall and Devon are not well forested now (think of Bodmin, Exmoor, Dartmoor), can't be sure what they were like 5K years ago.