It's a great bumper sticker. Ban foreign buyers! It's simple, it resonates and appeals to our sense of fair play: why should wealthy foreigners lock locals out of home ownership?

Photo: RNZ / Claire Eastham-Farrelly

But drafting legislation to enact the slogan is more complex. Now the holes - or the exemptions if you prefer - are emerging.

Ban foreign buyers! Except Australians. Ban foreign buyers! Except Singaporeans. Ban foreign buyers! Except overseas investors buying apartments off the plans in developments with more than 20 units. Ban foreign buyers! Except for Te Arai development, where iwi (25 percent) want to team up with a LA billionaire and a Queenstown property developer (75 percent) to sell luxury units to foreigners.

That last exemption made it into an initial draft of the Overseas Investment Amendment Bill before the Speaker ruled a public bill could not be used to benefit an individual.

That clause is now struck out - so no exemption for Te Arai. But the others will stand. Australian and Singaporeans get a free pass because of the way free trade agreements with those countries are structured.

As for foreign buyers in developments with 20 or more units they get to purchase apartments because to lock them out might have stopped the foreign investment needed to make the projects viable.

As varied as the exemptions are there is a common thread: in a small, open economy sometimes you need foreign capital to underpin a development. Locking out foreigners is a choice we can make but it has consequences. We may not be prepared to accept that but we should at least recognise it.

More fundamentally what is the problem we are trying to fix?

For the origins of this we need to go back to the early to mid-point of the decade when the Auckland housing market was accelerating at the alarming rate of 20 percent a year.

One of the most common anecdotes you would hear in Auckland at that time was the story of the 'Chinese buyer'. He'd be 'on the phone' at auctions. There'd be busloads of Chinese coming in from the airport to buy houses, according to another version of the tale.

How did people know whether these 'Chinese buyers' were third generation New Zealanders or recent arrivals? From Dunedin or Beijing? They didn't of course.

National initially refused calls to collect data on overseas buyers. So Labour did it for them. In 2015 Phil Twyford, now Housing Minister, released 'data' claiming up to 40 percent of Auckland property transactions involved Chinese. His 'evidence' was they had Chinese sounding names.

In 2016 National relented and got the data collected. It came back saying about 3 percent of sales went to foreigners. But that didn't stop the claims that foreigners - the anecdotes never seemed to include Americans or British - were outbidding us.

The claim shifted to say the Land Information data wasn't reliable, even though it was fairly consistent with each quarterly release. Labour changed the data collection agency to Statistics New Zealand.

The March 2018 quarter numbers from Statistics New Zealand showed pretty much the same thing, with foreigners buying about 3 percent of houses. And yes the figures are higher for Auckland (7.3 percent) and Otago (3.6 percent, boosted by Queenstown). But isn't that where you'd expect the apartments to be - perhaps the developments to be exempted from the new law anyway?

What about the Chinese buyer claims? Well, according to the official data there were 40,431 property transfers in the March quarter and 504 involved buyers from China - so about 1 percent.

This isn't the 1 percent we hear about when politicians talk about foreign buyers.

They use that number for 'the top 1 percent' - the elite. Minister David Parker tells us it's about values - that the top 1 percent shouldn't be able to outbid New Zealanders. And sure - it resonates.

But what happens when a one percenter joins up with iwi who want to maximise Treaty settlement by selling properties to foreigners? Or when a developer says a project won't be viable without foreign capital? That's when values smash into economic realities.

I saw this first hand making a TV documentary a few years back. We went to do a story about an American billionaire buying up wineries in Wairarapa. Local wine makers were going broke and in stepped the American billionaire. I went down with a TV crew expecting locals to be up in arms about the 'foreigner' buying up the land. But I couldn't find one voice raised against him.

There is one thing worse than a foreign buyer, they told me, and that's not having a buyer at all.

You can hear more the unintended consequences of the foreign buyer ban from RNZ's Otago report Timothy Brown on Insight, this Sunday morning at 8am

*Guyon Espiner is co-host of Morning Report on RNZ. He covered politics from the Press Gallery between 1998 and 2011 and produced the 9th Floor book and podcast series with RNZ's Tim Watkin.