When Bill English came into the NewstalkZB studio for an hour on the campaign trail, my co-host seized the opportunity. "If you're re-elected," Mark said, "will you bring in legislation banning single-use plastic bags?"
Talkback hosts all have their particular hobby horses and plastic bags are one of Mark's. Since we started working together 18 month ago, he has railed against the fact clean green New Zealand still hasn't banned plastic bags.
Bangladesh has. Rwanda has. Ireland introduced a levy on plastic bags in 2002 that meant 90 per cent of consumers were using reusable bags within a year.
Throw a dart at a map of the world and pretty much any country you hit has a ban or a tax on plastic bags.
English said his Government wouldn't bring about legislation in this country to ban plastic bags. He had faith private enterprise would take the lead without government intervention. Mark sighed and that was the end of that.
But it turns out English was right.
The market has prevailed.
Foodstuffs, the company that operates the New World, 4 Square and Pak'nSave brands, launched an initiative last month asking its customers what action should be taken on plastic bags.
And this week, opposition supermarket chain Countdown went one further.
It announced that from the end of 2018, single-use plastic bags would be banned from its Countdown, SuperValue and FreshChoice stores, which would remove 350 million bags from the environment every year.
Countdown's managing director, Dave Chambers, said they have been monitoring customer attitudes for the past couple of years and the most recent research indicated more than 80 per cent of their customers supported phasing out plastic bags in supermarkets.
Of course, we shouldn't be waiting for the Government or for business to take the lead when it comes to replacing plastic bags with reusable ones.
We could use our own initiative and take our own bags when we go shopping and indeed, many people already do so.
But although I have the best of intentions, it's usually only when I get to the checkout that I remember I should have brought a bag with me. I have fancy jute bags and canvas bags in my cupboard but they're absolutely no use there when it comes time to take my shopping home.
People tell me to leave the bags in the car but you have to bring the groceries inside, which means the bags come inside too - and once they're in the house, there they stay. I'm sure that when I no longer have an option I'll remember to take my reusables with me.
In London, when I was visiting my daughter and new grandchild, it only took a couple of visits to Waitrose before I understood it wasn't the done thing to turn up at the supermarket without a bag.
You could buy bags, certainly - but there was a thinning of lips and a furrowing of brows among fellow shoppers when I asked for bags.
There are lots no-nos in supermarkets in London, I discovered.
Not taking your own shopping bags.
Chatting to the checkout staff.
Offering to let somebody go before you in the queue. Funny lot, Londoners.
But they were on to it with the plastic bags.
By the end of the first week, collecting reusable bags from the drawer under the kitchen sink had become part of the routine of shopping.
Let's hope this is just the start of removing billions of tonnes of plastic from our environment. First the single-use plastic bags, then perhaps the unnecessary packaging of so much of what we buy.
Fifteen years after Bangladesh first saw the light and banned plastic bags, this country - which sells itself on and takes pride in being an environmentally friendly paradise - is finally catching up.
Kerre McIvor is on NewstalkZB Monday-Friday, noon-4pm.