It was bizarre, surely, that Mervyn King, governor of the Bank of England, found it necessary to devote a fair chunk of his Mansion House speech on Wednesday night to the vexed question of why the fiver in your pocket is a "soiled and scruffy" thing.
True, it gave him a cue to draw attention to a case in Wolverhampton Crown Court where the judge demanded to know why police failed for three-and-a half years to arrest a wanted Birmingham man when all the time he was living at home.
According to a newspaper report "Adam Smith, suspected of passing forged £20 notes, had a fixed address in Edgbaston and was picking up benefits".
So, when the Bank discovered so many Elgar £20 notes were being forged that it had to replace them in the Worcester composer's centenary year, it took the occasion to honour Adam Smith, albeit a different one.
One reason the tattered fiver lingers on is that it is not worth forging.
Few counterfeiters nowadays can be bothered to work for even a tenner a time, while some of us still give a £50 note a lingering look, which makes it a risky target.
So the £20 became the forger's favourite.
Governor King knows that the fiver has become a beer-sodden embarrassment.
The Bank has masses of crisp new ones stacked in its vaults.
The trouble is that the high street banks refuse to put them in their cash machines.
The Bank can distribute new ones only through Post Offices - and now state benefits and pensions are paid electronically that is a slow business.
Angela Knight, the feisty new head of the British Bankers' Association, made it clear yesterday that her members have not the least intention of helping.
A cashpoint passing out fivers runs out twice as fast as one spouting tenners, she pointed out.
They would run out more often, particularly at weekends and need twice as many visits from "secure couriers" to fill them up, with twice the security risk.
Eventually we will get a £5 coin. Coins have the economic virtue of lasting pretty well for ever.
They wear out after a couple of human lifetimes.
Even then, nobody takes the smoothed slice of metal back to the bank and asks to exchange it for a new one.
Every time the Royal Mint strikes £1 it makes £1.
The Bank hesitates for two reasons. First, coins are far easier to forge than bank notes. I have found two crude imitations of a £1 coin in my change already this year.
I had accepted them without a glance. A £5 coin would be well worth manufacturing criminally.
The second reason is that the existing £2 coin is so large and heavy that something worth two-and-a-half times as much would have to be enormous and wear out everybody's pockets.
The Americans once had a handsome (real) silver dollar the size of a British crown. But they used it only in the gambling state of Nevada, where it slotted nicely into the one-armed bandits.
Mind you, a silver £5 would be a neat little thing.
It would do fine - until the price of silver goes up and it is worth more than £5 melted down.