I've just read my gas meter, as I do every week, to feed the data into a spread sheet. My base gas load cost - standing charge, hot water for baths washing up etc. is around £5.50 per week - based on pre-October increase price.
By way of experiment, instead of using the central heating, I have been using the so far unused living room gas fire. It was installed new at the same time as the CH, simply as a backup for those occasions when the CH might fail.
Result of the experiment is that I have used the gas fire every evening, with door pushed to, not closed. Living room has often been warmer than I would normally have it, even on the 500w (judged by IHD) minimum setting of the fire. Cost has been a little over £1 for the entire weeks use, above base load cost. Temperature, which I continuously log, of the rest of the house never fell below 17.4C during the week.
For comfort, at the beginning of the week I swapped the summer quilt for the winter one and fitted the 90w under-blanket, set on max. That is plugged into a Smart Plug, so I can just tell Alexa to turn it on 20 mins before I retire, to pre-warm the bed. Must admit I have been warmer and more comfortable this week, than I would normally be, having the CH set to 18C for the entire day.