I know gas isn't your issue, but might help someone? We had a dodgy gas fire, it was either on full or off, but had it fixed and now we can turn it down to low. We put curtains up at external doors and use a draught excluder too. I have a fleecy throw and wear thick socks and a jumper/cardi all the time now. Luckily, DH and the DC are always warm.
The gas oven was always on, I'd cook meals for 2hrs+ now we cook double portions for an hour and freeze half, sometimes cook next day's dinner too. I also use the slow cooker more now.
We don't have GCH, so that's all the gas we use. By making the changes over this winter, we more than halved our gas use from this time last year.
The washing machine was on 2-3x per day, but now DH's work clothes are saved and washed together. Towels and T-towels wash together. Darks, mid-colours & whites are condensed to darks and lights. It's still on most days, but just once, which in turn uses less washing powder.
We dry clothes on airers or coat hangers in doorways. It took 2+hrs to dry one full wet load, costing 90p-ish in our dryer, that's now down to 15p for 20 minutes to just finish them in the dryer, so it costs the same for the week as it used to for one load.
Showering for less time, DH showers in record time and not 'forcing' the eldest DC to shower every day, he doesn't want to, that's his choice!
Finally, we've turned off the emersion heater. We estimate it will cost over £1 an hour (was on 2hrs per day) and it is a pain, but boiling the kettle 4x to clean/fill the sink should only be around 12p. We've only just started this, but we're hopeful it will show on the next statement.