Rishi Sunak's immigration plan comes at a huge cost that he isn't being up front about, says Nigel Nelson

The most important political quality is not hindsight but foresight. And the best politicians are those who possess it. Few do.

No decision by politicians can be taken in isolation because there is always a knock-on effect. And the mistake is to think solving one problem will never create others.

WATCH: Rishi Sunak on his migration plan

Donald Rumsfeld was US Defense Secretary during both the invasions of Afghanistan and Iraq. His most famous quote was widely lampooned as gobbledygook.

He said: “There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know.”

It wasn’t nonsense then and it isn’t now. It was a recognition that nothing is clear cut and the knack is to plan for all eventualities.

The Home Secretary may indeed reduce legal migration by 300,000 by raising the salary threshold for those from abroad who want to come here, and taking away the 20 per cent wage discount from employers looking for cheap labour in shortage occupations.

But the unintended effect he didn’t mention was higher prices. If builders, for instance, rely mostly on foreign bricklayers then they will face wages bills a fifth higher next year whether they continue to hire workers from overseas or recruit British ones instead.

Which will make the houses they build more expensive. And the same will apply to other areas such as welding, roofing and carpentry. It could even cost you more to take your pet to the vets.

That does not make Mr Cleverly’s decision wrong. Equal pay for an equal day’s work should be a basic right, no matter where you come from. But we must appreciate that all of us will end up paying for it in extra inflationary pressures.

The consequence of Mr Cleverly’s Rwanda plan, on the other hand, could be horrific as it may mean rewriting cherished human rights laws designed to protect us all.

The intention is not to leave the European Convention on Human Rights, just to ignore it, but an exit may turn out to be the result. So we should consider which rights we are willing to give up. The right to a fair trial? The right to free speech? The right to protest? The right not to be discriminated against?

And another unintended consequence was the resignation of the Immigration minister Robert Jenrick. Who thinks we should leave the ECHR. Even though Rwanda says they would abandon the deal if we do! Unforeseen result: utter chaos.

Not far from the GBNews studios, Boris Johnson has been remarkably - some would say uncharacteristically - honest at the Covid inquiry.

He accepts that had he acted differently lives might have been saved. He also accepts there was much in the early days he didn’t know, and also plenty he didn’t know he didn’t know - those unknown unknowns Donald R was banging on about.

The then PM was performing what he described as “an appalling balancing act” between the necessities of protecting public health and the needs of the economy.

Putting health first was clearly going to be economically detrimental. Eat out to help out was designed to help the economy but it also helped the virus to spread.

These unintended consequences would have been better dealt with had a bit more effort been put into foresight. But at least the ex-PM now admits that, which may prevent the same mistakes happening again.

But not thinking stuff through also affects other walks of life. Deaf sportsmen and women don’t get the same funding as those with other disabilities. They are understandably aggrieved that no one thought about this when the dosh was being doled out.

While it is true their speed on the track or skill with a football is not affected by whether their ears work, a sprinter will not be able to hear a starting gun nor a footballer the referee’s whistle. Or anything else going on around them.

Yet of the £612million UK Sport gives to Olympians and Paralympians, none of it goes to the Deaflympics or deaf athletes. That’s discrimination. The competitive disadvantages they face should have been foreseen.

Not foreseeing the unforeseen is not just a Tory problem. I have seen it throughout my three decades covering Parliament.

When Labour was in power it set a target that no one should spend more than four hours in A&E. And that goal was met more than ninety per cent of the time.

But the unforeseen consequence was that, to meet it, some hospitals moved patients to another part of the building before the deadline was up. They were out of A&E, but no less sick or in any less pain.

Which is why ministers need to be more aware of what they know they don’t know. And the really tricky bit - what they don’t know they don’t know.