When I worked in the Treasury, there were two unwritten rules about public spending. One was that ring-fenced budgeting was a bad idea, because it restricted government (read: Treasury) flexibility. The other was that targets based on a set amount of money being spent were also a bad idea, because they contributed to the notion that inputs were what mattered, not outputs, and hampered efforts to drive efficiency.

So, here’s an idea. The UK has two areas where it sets a firm spending commitment: 0.7 per cent of GDP on aid (to meet the UN target) and 2 per cent of GDP on defence (to meet the Nato target). Let’s add a third for education. A hard, minimum spending commitment, starting as soon as possible, and extending into the medium term.

The reason I like a spending target is threefold. First, it would allow schools to manage funding pressures. Although these are sometimes overstated (I’ll eat my hat if schools go down to four-day weeks), it’s undeniably tighter than it has been for many years. Second, it would mean government could make a serious punt at tackling social mobility, rather than just talking about it. Third and most important, it would be a tangible symbol that education was one of the UK’s enduring priorities.

There’s even a neat way of presenting it. Imagine Theresa May saying the UK government has three clear commitments: “We defend our nation through the defence target. We defend the most deprived in the world and promote global security through the aid goal. And today, we commit to defending the next generation and supporting our human security with a new education spending target.”

Let’s add a hard, minimum spending commitment starting as soon as possible

The high point of education spending was 5.95 per cent of GDP in 2009. By 2015, it was down to 4.68 per cent and by 2020, it’s predicted to be 4.07 per cent.

A reasonable target would be 4.5 per cent of GDP, which would take education spending back to about the level of 2016. If we assume schools would receive 75 per cent of all education spending (which has been consistent as a share since 2000), then this target would mean an additional £3.5 billion in 2018 and £5.9 billion in 2019. By 2020, government would be spending a shade over £7 billion a year more than projected.

These are, let’s be frank, huge sums of money. My former colleagues will be horrified. But everything is up for grabs post-Brexit. In his short, abortive leadership campaign, Michael Gove outlined some interesting thoughts about making education and science a real priority for the UK.

If we really want to change the way we do things, and to focus on a new set of priorities as an independent nation - and I don’t mean “politically really”, I mean “really really” - then it takes something of this magnitude. Over to you, prime minister.

Jonathan Simons is director of policy and advocacy at the Varkey Foundation. He tweets @jonathansimons