Labour’s manifesto includes a significant expansion in the size of the state, with the water, energy, mail, rail and bus companies all set to be re-nationalised. (The energy companies will only be partially nationalised but that’s a topic for another time.)

What seems to be confusing a lot of people is that Labour has not included any of those nationalisations in its accompanying document explaining how the manifesto will be paid for. Here’s why.

Under Labour’s fiscal rule, it has to balance day-to-day spending and aim for an operational surplus by 2022. That is to say, it can’t spend more on the regular functions of government than it takes in through tax. But it can borrow for infrastructure spending. To put it in real terms – Labour can’t spend money it doesn't have to pay doctors and nurses, or teachers. But it can borrow money - up to £250bn until 2027 - to build a new school or hospital.

Taking something into public ownership counts as infrastructure spend – just as Gordon Brown’s nationalising of the banks during the financial crisis did – under Labour’s rule, which is why the party doesn’t need to provide a revenue stream to do so. Just as spending on a new hospital secures a capital asset, so does nationalising something.

The counter-argument is that infrastructure spending creates jobs and improves productivity, but nationalising something merely changes whether those jobs are private or public. The Labour leadership’s view – and the one that would be tested if they won – is that by putting these assets into state hands, you unlock higher productivity and better job growth. (And, in the case of water companies, you gain tax revenue, as Labour’s shadow chancellor, John McDonnell, believes these companies are engaging in tax avoidance.)

And that’s why Labour hasn’t provided a cost for its renationalisation programme – and why, under its own fiscal rule, it doesn't need to.