I’m on our family summer holiday – this year, we’re in my hometown of Belfast. My mother has just turned 70, so we had a family get together here at my parents’ place to celebrate. I grew up in this house and there’s something terribly pleasing about seeing my boys enjoying playing with my old lego in my old bedroom.

Anyway our journey here involved driving from Newcastle to Cairnryan for the ferry. I practised what I preached and (for once) made sure the car’s tyre pressures were correct with noticeable benefits on the fuel gauge. We had a very pleasant drive, stopping at a great local salmon smokery/cafe/castle for lunch and got to the ferry terminal at the right time.

Everybody pulled up in their allotted queue, switched their engines off and wound down the windows. A few went off for ice creams. We were in queue 7 with at least 15 cars in each queue. Then something very strange happened. As soon as queue 1 started moving, everybody rushed to their cars, newspapers were stowed, windows raised – and started their engines. It took about 30 minutes for us to need to start ours, yet everybody sat there burning fuel unnecessarily, hunched over the steering wheel, despite the fact it was clearly going to be a while before we got moving and we’d have plenty of notice when it was going to happen.

Two things got me:

• The weirdly powerful peer pressure – the way the muted panic rippled across hundreds of people for something so trivial as being ready to drive on board. No one was going to miss the boat at this stage;
• The irrationality of keeping the engines running when it became clear that it was going to take some time to get moving – nobody seemed willing to ‘admit their mistake’ – would this have happened if other people weren’t there?

One of the things I’m working on in my constantly developing Green Jujitsu concept is how to harness these peer/group factors to produce greener behaviour – where everybody would feel comfortable leaving their engines off in this case. What would work? Countdown boards – “start your engines in 20 minutes”? Would that keep enough people relaxed enough to switch off that it would become the norm?

This sort of approach would take a lot of trial and error in each case – and would probably produce enough case studies to produce an entire sequel to the book Nudge. But there is power in peer pressure, and that means it is something we should be trying to exploit.

By the way, the ferry journey was notable for the diving gannets doing that wing tucking-in thing before hitting the water that I’d only ever seen in wildlife documentaries – amazing!