Iron fiscal rules that allow borrowing only for investment might seem like a sensible strategy, but the figures have repeatedly been fiddled to make the UK appear fiscally responsible. Both main political parties have been playing this game for forty years. From Thatcher onwards, Conservatives used privatisation and PFIs (private finance initiatives) to move debt off the public books to the private sector. Gordon Brown opted for the PPP (public–private partnership) model for the London Underground, and perfected the art by re-categorising some public spending (e.g. on health and education) as “investment” in order to meet the requirement to borrow only to invest.

The current approach, however, is much more serious. Governments are now borrowing to maintain our assets, calling this “investment”, as are the utilities. Fixing the school roofs and the hospital buildings, and, for the utilities, the sewers, the potholes, the sad state of the railway infrastructures, patching up the electricity networks, and maintaining the natural environment, should be current expenditure, not treated as new investments. We are borrowing from the next generation to pay for the current maintenance. Capital maintenance should be a current expenditure not a capital one.

Sustainable public finance would (with a few exceptions) require debt to only ever be for investment that genuinely enhances assets and creates new ones, such that the next generation receives better assets. When it comes to the environment, we need to pass it on in a good state, not to simply say we will continue to borrow and live beyond our means. Government needs to explain honestly and openly how it will balance the books. Pretending that our fiscal rules are held with an iron fist whilst actually including the capital maintenance is bad accounting. The numbers are huge. The next debt crisis will follow as the unsustainable is not sustained.