National’s tax plan debacle is looking more and more like an episode of Grand Designs.

A wide-eyed optimistic couple with a big dream. They reckon they’ve done the numbers and can definitely make it work. But, as time goes on, some people start raising their eyebrows and asking a few questions and the shiny happy people start getting all defensive on it.

But then, as we all know, most times we find out that people were right to be raising their eyebrows and the numbers never stack up.

Another situation you could compare National’s tax plan debacle to is when, again, a wide-eyed optimistic couple with a big dream, fall in love with a half-renovated villa and convince themselves that even though the people selling it have run out of puff, they can turn things around and get the renovation back on track.

And again, like the Grand Designs situation, when they start telling other people about their big vision and every Tom, Dick and Harry starts chiming in with their opinion, the wide-eyed couple start to feel under attack because people start telling them what they don’t want to hear. Or people start asking tricky questions.

People want to know how much they reckon it’s going to cost to finish the renovation. They get people pulling holes in their estimates or telling them that, instead of taking on a half-finished villa, they should be doing something less risky and looking for a sensible brick and tile with aluminium joinery.

And, again, like on Grand Designs, the wide-eyed couple get sick and tired of people poo-pooing their ideas and they get all defensive and they just don’t want to talk about it anymore. Even when they know, in their heart of hearts, that a big part of what they want to do is all wing-on-a-prayer, hoping for the best, it’ll all come out in the wash.

Because where there’s a will, there’s a way! Right?

Well, that approach might be fine for renovating a house. It’s a completely different story, though, when it comes to renovating an economy.

And so, yesterday, we had three economists from across the political divide coming out with their analysis of National’s tax plan. And they reckon National could be over-cooking the numbers to the tune of nearly $500 million per year.

They are former economist Sam Warburton, former Reserve Bank head of financial markets Michael Reddell and Corelogic head of research Nick Goodall.

And what they’ve done, is they’ve spent hours over the past couple of weeks doing some modelling work on National’s plan to tax foreigners buying property here. Which is one way National plans to fund its tax changes.

These three economists have looked at three different scenarios and reckon this part of National’s plan would be more likely to bring in between $212 million and $286 million per year. A lot less than the $700 million National is saying that it’s going to raise.

So these experts are saying the gap between National’s numbers and their numbers is between $450 million and $520 million a year. Or around $2 billion over the next four years.

But National's Christopher Luxon and Nicola Willis aren't budging and say they've released all the detail we need to see and we just need to trust them to deliver.

Now I’ve doubted National’s numbers on the foreign house buyer thing right from the start. And the numbers that came out yesterday back me up on that.

I also think National is overcooking the numbers when it comes to the money it thinks it’s going to save on public sector spending.

That’s because when Christopher Luxon was here the other week, he couldn’t tell me when current contracts end for all the consultants and contractors he wants to get rid of. If he doesn’t know that, then he has no idea when he can achieve those savings.

And then we had Nicola Willis making the big claim this week that she reckons the public service cuts can be made by Christmas. Which means it won’t be the consultants that get the chop first. It’ll be public service staff who go.

The thing is, though - and I didn’t always think this would be the case - but I think they’re going to get away with this smoke and mirrors behaviour because there seem to be enough people out there who seem to think a change of government is more important than facts.

And it’s not even people thinking about their own wallets. It’s people so obsessed about getting rid of Labour. And the tragedy of all that, is that they even seem to be willing to turn a blind eye to National’s smoke and mirrors, if it means getting rid of this current government on October 14.

I’m just as tired of the current Labour government as the next person. But where we differ, is that I’m not going to fall for the wing-and-a-prayer promises from National, if it’s not going to front up with the facts.