A fine or a nudge? Charging for plastic bags works and is an interesting behavioural case study

I’m sure you can empathise: I was just about to exit my driveway to head to the shops when, with a pang of annoyance, I realised I’d forgotten my bags-for-life. 

Cue a slightly irritating 2-minute process of removing my seatbelt, turning off my ignition, unlocking my front door (double bolted), rummaging in the cupboard, re-locking the door, and back to the car I went.

Not a major hassle (first-world problems and all that), but still a surprising amount of effort to save myself 10p. I don’t think I’d even stoop to pick up 10p off the pavement, yet somehow, over the last seven years I’ve acquired don-level skills in Grocery Jenga and creative use of pockets (is that an aubergine….?) to manoeuvre my bagless shopping out of the supermarket

New data from the UK’s Department for Environment, Food and Rural Affairs would suggest I’m not alone. The charge for plastic bags introduced in 2015, 5p initially and recently ratcheted up to 10p, has led to a massive drop in usage of 97%. The average shopper in a UK major supermarket now uses just three plastic bags per year, compared to 140 back in 2014.

Impressive indeed. The only behavioural intervention we know of that can reliably achieve effects anywhere near that size, short of all-out bans, is a default. That is, opting people into the desired behaviour automatically. So how can such a small incentive (10p for a bag which might typically carry  anything from £5 to £20 or more of shopping) be so effective?

The answer lies in the fact that incentives almost always bring psychological baggage too. They change the way we perceive options, beyond the narrowly economic dimension:

• The plastic bag levy is, in fact, a default. You now have to proactively ask for a bag against the presumption that you don’t need one. Pre-2015, if you brought your own bags to the shop you’d best say so quickly, before the cashier started frantically peeling single-use ones off the rack.
• The plastic bag levy is a timely prompt. We all know plastic is bad, and already want to use less of it, so being constantly reminded to act on these intentions is quite useful.
• The plastic bag levy is a social norm. The levy, and the wider plastic-awareness it has helped to instil, makes the act of asking for a bag a far more salient social taboo (breaching an injunctive norm). How often have you apologised to the cashier for forgetting your bags? Oh the shame!
• The plastic bag levy is salient. Costs can be relatively hidden or made explicit and painful (like paying in cash compared to on credit card). In this case, the act of paying for something to which we ascribe no real value, and used to get for free, means it stings a little more.

So it’s a wonderful example of a behaviourally-informed incentive. I’d argue that these behavioural dimensions are likely to be doing far more of the work than the economic incentive itself – so would classify this as more of a nudge than a fine.

But it’s a useful behavioural case study for another reason too – reminding us of the need to measure impacts broadly. How many of us now buy more bin bags because we don’t have lots of old shopping bags? And when we do occasionally buy a plastic bag, they’re thick and sturdy, and so the amount of plastic it contains might be orders of magnitude higher.

This doesn’t undo the positive impact of the levy, but it does serve to highlight the importance of spill-over behaviours and backfire effects, which we should always be sensitive to in all our efforts to encourage sustainable behaviours.