They don't age gracefully
When did you last see a lovely crisp five pound note?
The nation's stock of the lowest denomination of promissory notes is becoming increasingly grubby and tattered because they are staying in circulation far longer than they should.
While the respect we show £50 notes means they can last for three to four years, we're far rougher on the poor fiver - which correspondingly has a life expectancy of just nine months.
Unfortunately, the smallest notes are not finding their way back to the Bank of England often enough to be replaced with freshly-printed versions.
"People use them so much, rather than deposit them at their bank. We've been looking at the problem of note quantity and quality for a while now," says a Bank of England spokesperson.
Paper tiger
All notes are printed on durable cotton fibre paper - which also gives them a hard to counterfeit crisp feel. But even Portals, the paper supplier since 1724, cannot make an indestructible note.
To halt the fiver's deterioration, the central bank has enlisted the help of High Street retailer Marks & Spencer and the Post Office to swap old notes for new whenever possible.
The scheme seems to be working, says the bank, with dog-eared and fake fivers being gradually filtered out of circulation.
And good thing, too. If they change hands enough, banknotes can be tainted by all sorts of things. A BBC survey suggested that 99% of the £24.7bn of notes in circulation in 1999 had traces of the drug cocaine on them.
Notes shredding with age can also be a pain for shoppers and store owners alike. West Africa suffered an acute shortage of the smaller local francs last year, thanks to the European printer devoting all its presses to making euros.
With the existing notes in tatters, traders furiously hunted coins to give their customers in change. Churches reputedly did a roaring business swapping big notes for the coins from their collection boxes - and adding a handling fee, of course.
Fading fiver?
Becoming tatty is not the only crisis facing our fiver. The once popular blue notes are falling out of favour with some.
Automatic Teller Machines (ATMs) are now rarely filled with the small notes - since by only offering customers larger denominations the banks can restock the machines less frequently.
So why not wave goodbye to the fiver altogether and replace it with a coin?
Coins have a life expectancy measured in decades rather than months. For instance, two-shilling coins bearing the head of King George VI were still being used as 10 pence pieces more than 40 years after his death.
In the United States, the authorities are desperate to encourage citizens to warm to the new $1 coin and give up the familiar "greenback" paper dollar. If all the paper notes go, the nation could save an estimated $500m every year.
"We have no plans to introduce a £5 coin," says the Bank of England. "In fact, we're preparing to launch a new note design - with Elizabeth Fry on it - this summer."