Boris Johnson's biggest Brexit promise has just been exposed as a red herring

A key pledge made by Boris Johnson to Brexit supporters was that leaving the European Union would mean the UK could launch its own Australian-style points-based immigration system and “take back control” of our borders. If Brexit means anything, it means a points-based system — and soon.

This promise made a simplistic appeal to the public. Want borders controlled? Then a points system will do this. Don't want low wage workers coming in? A points system could block their entry. Some evidence found the regular appeals to an “Australian” model, instead of others in Canada or New Zealand, appealed to those who wanted less immigration of non-white migrants (irrespective of how Australia's system actually works).

As the UK prepares to leave the EU on Friday, the prime minister has reaffirmed his pledge - also repeated in the manifesto that delivered him a majority in December's general election - that our immigration system would become points-based as a clear sign of his government "getting Brexit done". Last September, the Migration Advisory Committee, which supplies independent, evidence-based advice on immigration to the home secretary, was commissioned by Priti Patel to review specifically how an Australian-style system could be introduced and launched in Britain.

The resulting 278-page report, published yesterday, has blown a large hole through Johnson and Patel's promises.

First, Brexit is not needed to introduce such a points-based immigration system. It is a rarely acknowledged fact that the UK has actually had an Oz-inspired system since 2008, first launched by New Labour under Tony Blair. No Brexit is required to run a points-based system after all.

Second, the committee admits it (and, we might therefor assume, the government?) possess insufficient data and knows "very little about how the system for settlement works” - more reason why the committee's membership must be expanded to include law and social policy experts. So there is no clear evidence that a system can be designed to meet the government's objectives - and almost certainly not by December this year.

Third, the committee rejects outright a points-based system for all. That sort of scheme is not used anywhere else, even in Australia. But it does support retaining the current Tier 2 professional points-based system with a small reduction in the mandatory salary threshold. The only area that should have a system introduced is the relatively rarely used Tier 1 exceptional talent category, where the impact would be slight. Oddly, low-skilled migration is not mentioned despite being an area repeatedly singled out as requiring change.

How has the government taken this news? Not well, starting with the sacking of the committee's chair, Professor Alan Manning, who will continue for a few months to answer questions arising from this report but not renew his three-year term as he had desired. Clearly, Number 10 only wanted to hear that their fact-free voter promises can be realised simply and effectively, rather than have hard evidence cut through their fantasy land election pledges. All the more important, then, to have an evidence-led, independent body that can provide the relevant context needed for policy-making, warts and all.

Such work should have been done before the pledge became a cornerstone of the promised Brexit, or at least by the time of the general election. The problem for the government is they've raised expectations too high that a new system will come close to delivering on slashing net immigration and boosting British jobs for British workers. Instead, the expected effect on wages and employment opportunities for these workers is close to zero — and yet this change was vowed to be a major, positive transformation. Both sides can't be right.

Johnson has U-turned on this issue before. When Theresa May ruled out introducing a points-based system when he was foreign secretary, Johnson said the crucial thing was to take back control, not how this was done by any particular system.

While EU migration has declined since the referendum, non-EU migration through the current points-based system reached its highest ever level during the last election campaign. Taking full control has not meant less migration even for non-EU citizens using a system the government wants at the centre of all immigration decisions.

The government is not only reinventing the wheel, but seeking to recreate a less effective version of its model inspiration. This is bound to damage public trust on immigration further when pledges are broken or fail to deliver on any of their promised benefits - with those who simply state the obvious, like MAC's chair, promptly dismissed from their posts.

This is a government in crisis. If the one key Brexit pledge is a red herring, this bodes worryingly for what is to follow next. Perhaps Brexit was a useful issue for gaining electoral advantage, but its implementation and consequences on its most fundamental positions have yet to be thought through.

Thom Brooks is professor of law and government at Durham University