AFAIK the only domestic Gas tumble-drier is the White Knight.
very cheap to run but has to be installed by a qualified gas fitter
In Which tests the White Knight ECO 43A  (£280, timer) and 83A (£310, sensor) were both Best Buys
Report on the 83A says:
"White Knight may not have any Best Buy electric tumble dryers but their two gas powered machines dried very quickly and evenly in our tests and are worthy Best Buys.
The Eco 83A uses a sensor to monitor how dry the load is, it has a 7kg capacity and takes 127 minutes to dry a full load of cottons. Because it uses gas to provide the heat for the drum, running costs will be significantly cheaper with a gas dryer compared to an electric model. This is certainly something to consider if you regularly use a dryer.
Drying performance was equally impressive on both cottons and synthetics. Along with standard cupboard dry, iron dry and extra dry programs for synthetics and cottons, there’s a cold airing program to cool your clothes down after drying which makes them easier to handle. There’s also an anti-crease cycle which gently tumbles clothes without heat after drying. In common with the Eco 43a, you can position the door hinge on either side.
Pros – Drying performance, ease of use and lower running costs than electric models.
Cons – Gas powered dryers will need to be professionally installed and serviced by Corgi engineers."
very cheap to run but has to be installed by a qualified gas fitter
In Which tests the White Knight ECO 43A  (£280, timer) and 83A (£310, sensor) were both Best Buys
Report on the 83A says:
"White Knight may not have any Best Buy electric tumble dryers but their two gas powered machines dried very quickly and evenly in our tests and are worthy Best Buys.
The Eco 83A uses a sensor to monitor how dry the load is, it has a 7kg capacity and takes 127 minutes to dry a full load of cottons. Because it uses gas to provide the heat for the drum, running costs will be significantly cheaper with a gas dryer compared to an electric model. This is certainly something to consider if you regularly use a dryer.
Drying performance was equally impressive on both cottons and synthetics. Along with standard cupboard dry, iron dry and extra dry programs for synthetics and cottons, there’s a cold airing program to cool your clothes down after drying which makes them easier to handle. There’s also an anti-crease cycle which gently tumbles clothes without heat after drying. In common with the Eco 43a, you can position the door hinge on either side.
Pros – Drying performance, ease of use and lower running costs than electric models.
Cons – Gas powered dryers will need to be professionally installed and serviced by Corgi engineers."