Horticultural charcoal is an incredibly exciting product.
fine chips of charcoal have a number of uses round the garden . They can be used in the bottom of pots and bottle gardens to keep the soil sweet and retain moisture . They can be spread round Hosters to keep the slugs off . I have also sold some to the National Trust at Townend to combat a disease of their Box hedge , although I'm not quite sure how it works .It can be put into socks then put in the garden pond to control excess nitrates in the water. Generally charcoal appears to be the Holy Grail of soil additives but don't take my word for it here is a link to a Cornell University website.
The price for horticultural chips ( less than half an inch to greater than quarter of an inch) is 75p a kilo. I have sent this by post but the postage ends up more than the charcoal.