I'm not sure what the situation is with gas fires, but a wood burner wouldn't usually have any requirement for a power supply, so can operate completely independently of whatever else might have occurred (power cut, central heating not working, excessively chilly, etc...). If your central heating runs on gas it also provides you with an opportunity to balance your heating costs a little between the two fuels depending on cost, or other factors. I currently pay about 6 to 6.5 p per kWh for reprocessed wood fuels (as pellets), you would probably pay a bit more for smaller quantities, and logs/briquettes may be a bit more too. I've no idea how the cost of gas would compare, although I wouldn't be surprised if it is cheaper. If you burn reprocessed wood you won't be a townie wood scrounger, and it is certainly a lot less hassle than real wood and probably not much more costly either if you don't have your own supply.