Regular readers will know I’m a bit sceptical about the plastic bag tax – mainly because it’s aimed at a minor environmental impact rather than a major one such as home insulation. But what I can’t argue with is its effectiveness, with Tesco (the UK’s biggest retailer) announcing that plastic bag use had fallen 78% within a month of the tax coming into force.

And I’m quite surprised at the change it has made in my own behaviour. I’ve endeavoured to take reusable bags to the shop with me for 25 years, but I all too often forget. Strangely enough, the thought of having to pay 5 or 10p for a bag has sharpened my memory and I go much better prepared. The proof is in the pudding – the once huge stash of plastic bags under the sink is dwindling fast.

The difference really hit me yesterday – I had to do an unexpected grocery shop between meetings as old friends announced they were visiting out of the blue. I ended up cursing myself for not having a reusable bag with me always in case of such a situation.

This goes to show the power of adding even small amounts of friction to habitual unsustainable behaviour. It’s classic ‘nudge’-style behavioural change – remove obstacles to desired behaviour and throw a few in the way of undesired behaviour. Very rapidly people will adjust their behaviour to the path of least resistance.