Wood can be burned in a smokeless zone if the appliance (i.e. the stove or boiler) has an Exemption Certificate. Companies which manufacture stoves with Exemption Certificates include Clearview, Vermont Castings, Dovre, Dunsley Yorkshire Stoves, Morso and Jotul. A full list can be found at www.uksmokecontrolareas.co.uk
Obtaining an Exemption Certificate is an expensive and lengthy process. There are currently no pellet burning stoves or boilers that are on the exempt appliance list, although many are tested to a high standard in their country of origin.