If you have the will and patience, then try and find a local British woodland charcoal maker. Up to 90% of charcoal sold in the UK is imported and a large portion of that comes from Paraguay, which borders Brazil. Prime rainforest is disappearing at an alarming rate & charcoal burning is a contributor to this.
It's easy to overlook, but it is important. Waitrose is now sourcing much of their product from Kent & Cornwall, which is produced from sustainable & well managed British Woodlands. The demand for home produced Charcoal is on the rise.
Support your local producer and help an ancient craft re-establish itself in our woodlands, even better go and visit them, see the process in action.
Lastly, high quality charcoal is sold in volume. The ligher it is, the better the carbonisation, the quicker it heats up. Plus the flavour is fantastic.

Surrey county council have a list of charcoal makers on their website.
http://www.surreycc.gov.uk/environment-housing-and-planning/countryside/woodlands/woodland-products/charcoal