It would be a stretch to describe the latest report from Wrap, the government’s waste advisory body, as riveting reading. The UK Voluntary Carrier Bag Monitoring: 2013 Data is light on jokes, bodice-ripping and sword-and-sorcery thrills, but for those of us fascinated by the psychology of behavioural change, it beats George RR Martin into a cocked hat.

In Northern Ireland, which introduced a compulsory 5p charge on plastic bags last year, there was a 71% drop in consumption. In England, which has yet to implement such a rule, usage rose by 5%. Meanwhile, Wales, which brought in charges two years ago, saw its similarly precipitous fall go into reverse, with a rise of nearly a fifth. It seems the immediate change in behaviour reaped by the new charges is short-lived and it doesn’t take long for old habits to re-emerge.

This is something that could have been easily predicted by behavioural scientists. In a classic paper from 2000, Gneezy and Rustichini studied what happened when day-care centres in Haifa, Israel, tried to reduce late parental pick-ups by introducing fines. Before long, late pick-ups had not reduced, they had doubled. Why? Because parents felt that the fine was a price worth paying and the guilt which had previously controlled their behaviour was assuaged.

While attaching a cost to something that was free certainly reduces frivolous consumption, cost that is too low can merely act to pay off one’s conscience. On the other hand, as Robert Cialdini famously noticed, price an item highly enough and that price creates its own value. When Sainsbury’s sold a limited edition Anya Hindmarch reusable shopping bag for £5 in 2007, customers queued from before dawn to buy them and they changed hands for up to £200 on eBay.

Major retailers have a huge incentive to keep us using their bags. Every one is a miniature billboard being carried up and down the street. Alongside charging customers for bags, there is surely an argument for taxing the companies for every bag they distribute, and charge them more if they brand it with their logo and name. Personally I’m not convinced that the damage done to the environment by plastic bags, in comparison with the gargantuan waste of the food chain as a whole, is commensurate to the attention the issue attracts. Nonetheless, I stubbornly stuff my tins of beans into an old rucksack in preference to volunteering to act as a sandwich board for a multinational supermarket. I’m bloody-minded like that.

The most striking detail about the Wrap report, however, is that between 2006 and 2009, long before charges were contemplated, there were dramatic falls in plastic bag use across the UK – motivated not by finances but by consciences. Despite a slight recent upturn, plastic bag use by weight is down 39% since 2006. Appealing to people’s consciences reaps rewards, up to a point. The extent to which environmental awareness in itself leads to changes in behaviour is, however, questionable. One of the more depressing truths for anyone with green leanings is that awareness of problems does not in itself change behaviour. People who learn about the importance of energy conservation do not conserve energy.

The usual advice on encouraging sustainable behaviour – reinforcing self-image and identity, for example (“I’m a good person and good people reuse their shopping bags”) – can rather fall down when one is already spending money in a supermarket. What is likely is that the sudden spurt in people opting for a “bag for life” and other alternatives to the heaps of gossamer thin carriers occurred not because of sudden concern for the planet or self-interest, but plain old herd behaviour. A social norm emerged which meant we expected ourselves to find an alternative to endless plastic bags. We did it because everyone else was doing it and everyone else was doing it because we did.

There is a lesson here, perhaps, not just for those who fret over the humble placcy bag, but for everyone wanting to change our habits relating to our health, our diet, our lifestyle, our carbon footprint, even our criminal offending. In an echo of the worst cliche of the fashion industry, darling, simply everyone is doing it. Even if it is not true today, it soon will be.