When the mandatory 5p charge for plastic bags was introduced in October last year, the hope was that it would change behaviour in Scotland, as it has done already in Wales and Northern Ireland, but no one could have suspected how quickly and profoundly it would do so.

According to retailers and campaigners, since the introduction of the charge six months ago, the use of plastic bags has dropped by between 80 and 90 per cent. That is an astonishing change, but it has also raised thousands of pounds in good causes, with many shops passing on the money collected to charities and community groups.

The 5p charge also represents a spectacular success in an area of environmental concern that needed drastic action. For too long, shoppers thoughtlessly used plastic bags for just a few items. The sight of the bags littering the streets and the countryside had also become a depressing sight, and the bags represented a considerable threat to marine life (and still do).

Five pence per bag is not much to pay to help fix these problems, but better than that: shoppers seem to be changing their habits quickly. The change in the law is also an example of the kind of nudge that governments can sometimes give citizens - in this case, we have all been nudged towards a greater sense of environmental responsibility.