Labour have been good at abusing the word investment. Traditionally it refers to a decision to spend money on equipment or property that allows you to supply goods or services over a period years. This spend can be accounted for as capital spend, with building or equipment included as an asset in the balance sheet. If an enterprise spends more on employing people or on energy that is a running cost to be included as a cost in annual accounts.
You can argue that spending on training or research is an investment as they may yield benefits in future years that add revenues.
If you do spend on capital items you often have to borrow to pay for them. You put both the value of the item and the loan to buy it on the balance sheet. Businesses expect to earn sufficient money by having an extra machine or a bigger building to be able to pay the interest on the loan to buy them, to repay the debt over a period of years and make a profit.
The government often makes investments that cannot do this. It may be good to build a replacement school but there will be no extra revenue to pay the interest on the debt or return a profit. Plenty of investments in free services paid for by taxes need some other way of appraising their contribution.
The state also makes investments that can and should be appraised like private sector investments. New railway lines need to generate new and additional rail revenue to justify their capital costs. Green investments by Great British Energy or the National Wealth Fund need to be cash generative. I will discuss how in a future blog.