Average gas bill estimates are only really going to apply to you if you can compare your situation with other households that have the same amount of rooms and have the same amount of occupants.
A single person living in a flat would probably be using approximately £10 per week in gas but even this can vary depending on whether they have an electric cooker and use gas or electric means of heating their property.
Similarly it would probably be around £20 to £30 per week for a four to five bedroom house with a family living in it but again there are many variables which could affect this estimation.
Of course with the UK you also have to allow for our weather which can be varied at the best of times and usually we end up with 6 months of bad weather and then 6 months of winter(only joking).
Average gas bill estimates can also be hugely affected by the energy company you are using too as there are now so many competing companies available with different plans and schemes that getting a true average between one home and another is virtually impossible on a level basis.
I would assume that if you are looking for an average gas bill price then you are probably concerned that you feel the amount you are being charged may be too much and if this is the case then the best advice I would be able to offer is to try a comparison site where you can compare your gas and electricity bills against the most competitive available.
The process of comparing your bills only takes a few minutes and who knows you could find a much more competitive energy supplier that can save you money every month.
So with a view to getting your average gas bill figure why not go to a comparison site now and get a free quote showing you what companies are available and how much they will charge, it could be the best and most rewarding few minutes you will spend on the internet.