I weighed the rubbish bag again yesterday afternoon, so a week after last emptying my bin, and it was still barely 2 pounds, and less than a kilo.
We'll have to see what the coming weeks bring. I haven't made any special efforts, yet last Autumn I felt it would be far too much trouble to try the challenge. As I said before, what I have done is gradually change my attitude to rubbish and waste in general over the last few years.
Realising that most of the bulk of my bin was made up of plastic bags, I've set aside some plastic packaging I acquired yesterday, which says it is recyclable and made with plastic no.4: low density polyethylene used for carrier bags and bin liners. So that kind of plastic should be fine to put in the carrier bag recycling bins. I'll try and watch out for it in future.