In reply to girlymonkey:
You can use smokeless fuel on a multifuel stove. The common house coal, is bituminous coal. This can cause one or two problems. The most dangerous is when the fire is covered in coal with no flames showing. A thick greasy greeny yellow smoke is produce, which has a high concentration of coal gas in it. When the flames do get though, if there is any air above the fuel load this mixture can explode violently, all the way up the flue. I have seen the end blown out of a property as a result of this. If it does not explode it will deposite bitumen, creosote and tar up the flue which will either restrict or block the flue, sending dangerous and very toxic flue gases (Carbon monoxide) back into the property, or catch fire and cause a lot of damage to the flue.
I used to be a consultant for the National Solid Fuel Advisory Service, and the British Flue and Chimney Manufacturers Association, and had to report on many instances of these problems/events, some causing fatalities.
Stick to wood, smokeless fuels and manufactured wood fuels as per instructions.
Post edited at 11:10