In 1751 the Bank of England began selling a bond with no repayment date on it. Not a distant date. None at all. You handed over your money, the government undertook to pay you interest twice a year for as long as there was a government, and the principal stayed where it was, permanently. Consolidated annuities, shortened almost at once to consols.

A perpetual bond asks something unusual of the person buying it. You are not lending against a date, because there is no date. You are buying a position in the continued existence of the institution, and the only way the arrangement ever ends is if the borrower chooses to end it or stops being there at all.

The year after the first issue, Henry Pelham swept the outstanding government stocks into a single bond at three and a half per cent, chiefly to get the coupon down. In 1757 it came down again, to three. It stayed at three for the next hundred and thirty-one years. A rate held that long stops being a number and becomes a piece of furniture.

By the middle of the nineteenth century the consols were less a financial product than a feature of the English weather. Austen's characters keep money in them. So do Thackeray's, Dickens's, Forster's, Galsworthy's. When a novelist wanted you to know that a woman was provided for and could not be ruined, he wrote that her money was in the consols, and the reader understood the whole of it at once: no upside, no anxiety, an income until she died and then an income for whoever came next.

Then, in 1888, George Goschen converted the three per cents into a new two and three-quarter per cent stock, which stepped down to two and a half in 1903. Inside that conversion sat a clause that quietly changed what the instrument was. The new stock carried a first redemption date of 5 April 1923. From that morning onward, Parliament could buy the whole thing back at par whenever it liked.

It did not, for ninety-two years.

Look at what passed through that window. A general strike. The exit from the gold standard. Churchill, as Chancellor, issuing a fresh four per cent consol in 1927 to refinance war bonds from 1917, answering one endless promise with another one. A second war. The end of an empire. The nationalisation of the Bank. Decimal coinage. Every Chancellor across that span held a live option to close the account, and every one of them left it open.

The reason is duller than honour and more interesting than neglect. While the cost of borrowing was high, the old stock was extremely cheap money. A government paying two and a half per cent on paper issued before anyone had thought of the telephone is doing very well out of it, and the sensible thing is to leave it exactly where it sits. The promise survived because keeping it cost less than ending it.

Eventually the arithmetic turned over. In October 2014 the Treasury announced that it would redeem the four per cent consols in full, and did so on 1 February 2015. The three and a half and three per cent stocks went between March and May. The last of them, the two and three-quarters and the two and a half, were redeemed on 5 July 2015. Section 124 of the Finance Act 2015 swept up the legal remains.

Nothing had changed about the meaning of the debt. What changed was the price of money. Borrowing had become cheap enough that four per cent in perpetuity was no longer a bargain but a standing expense, so the Treasury exercised the option it had been holding since the spring of 1923, for exactly the reason nobody had exercised it in ninety-two years. It had become the cheaper thing to do.

There is no scandal here. Holders were paid at par and nobody was cheated. When the Treasury announced the repayment it made a point of the ancestry, noting that some of what was being cleared could be traced back, conversion by conversion, as far as the South Sea Bubble. That is the sort of detail that gets read as reverence. I think it is better read as an accounting note that happened to be very old.

We like to describe long commitments as though they are held in place by character. Endowments in perpetuity. Cover for life. Treaties with no expiry. A structure maintained indefinitely. The consols are the longest clean run of evidence anyone has on how a promise of that kind behaves in practice, and the finding is unsentimental. It was kept while it was cheap. It was reviewed when it became dear. It was closed by a numbered section in a Finance Act, and the section did not mention what any of the money had originally been for.

The useful half of the lesson is the other side of the same fact. For almost all of those two and a half centuries, the cheap course and the honourable one were the same course, and that was not luck. It is what Pelham and Goschen built, most likely without intending to. A promise that survives is one whose terms keep making it the easy option, decade after decade, for administrators who never met the person who made it and feel nothing in particular about him. Resolve does not last two hundred years. Structure sometimes does.

Britain has nothing on its books now without a date. Everything the state owes, it owes to someone specific, by a specific day, and when the day arrives the relationship is finished and both parties go away. The consols were the last item on the ledger that was never going to end. They ended when they got expensive, which is how most things end. It took two hundred and sixty-four years to find that out.