I asked how Treasury officials, at spending reviews or budgets, placed a value of £1 spent by different Whitehall departments. For example, £100 million given to the NHS would deliver some value for that spending, how does that value stack up against £100 million spent by DESNZ?

The reason why I recall that exchange is that over the past few weeks we have seen various attempts to second-guess what might be in the budget due this autumn. I’ve read about a number of new taxes, some new ways of levying tax and plenty of ways of spending it. But nowhere in this discussion so far, have we actually asked what value have we got from such spending.

Turning to UK heating policy, heat pumps have now been subsidised by the government for over 14 years. Aside from the obvious question, how many more years, what value has been obtained from the spending?

The importance of this question is that the size of the subsidy has grown significantly of late and is due to grow even more in the future (at least until 2029). Just looking at the 12 months up to the end of June here is my list of subsidised heat pump expenditure (either via taxation or bills):-

ECO £245 million; BUS £209 million; SHDF £33 million; HUG £49 million and an estimated VAT subsidy of £156 million – a total of £692 million in 12 months.

My point is not to criticise this spending, others may do so, but to ask how does the Treasury place a value of spending £692 million this way against the many other priorities it will have? How do politicians make judgements on whether this is a good use of the cash is a similar question. It’s the classic ‘guns v butter’ argument that you first encounter studying economics. A difficult question but one that needs answers.