When will old £5 notes become worthless? What should you do?

The new plastic £5 notes have now been in circulation for four months, but what about the old, tatty, paper ones? There are still millions lurking in wallets around the country, and we'll need to find them fast, because it's not long before you won't be able to spend them any more.

See also: Everything you need to know about new £1 coin

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The Bank of England introduced the notes in September, and we have until 5 May 2017 to spend the rest of the paper ones. It gave us eight months to dig out and spend our old notes - and half that time has already gone.

The Bank says we have spent roughly half of the old notes in circulation already, but there are still £165 million of them in piggy banks, old wallets, and down the back of the sofa cushions. If we don't get round to spending them by 5 May, they won't be 'legal tender', so we won't be able to spend them in shops any more.

Will they be worthless?

The good news is that at this point, if one suddenly shows up at the bottom of a bag, you should still be able to take it into any bank, building society or post office to exchange them. Banks may start to turn their noses up at them eventually, but the Bank of England is legally obliged to take the notes forever.

They will do so free of charge either in person or by post - so you don't need to make a trip to London if you find an old £5 lurking in the pocket of an old pair of shorts this summer. If you're doing it by post, you need to complete an exchange form, and decide whether you want a new note sent out to you (as long as there's no more than £50 worth of notes to be exchanged), a cheque in the post, or the money credited to your bank account - which should be there within ten days.

Clearly if you find your old £5 notes sooner rather than later, it's going to be easier to spend them. It means it's worth making time over the next few months to have a clear out of old bags, coats, jackets, money boxes, drawers, down the backs of sofas - and indeed any other spot where cash might be lurking around your home. It's also worth checking any nooks and crannies where you keep money in the car for paying for parking.

Do you have to accept them?

Meanwhile, if you are handed an old £5 note in your change, you are within your rights to refuse it and insist on a new note or coins. The Bank of England points out that what you or any shop decides to accept from one another is entirely a matter of discretion. Just as a shop is within its rights to refuse to accept £50 in payment for a single banana, you can refuse to accept an old £5 note in your change. Both are technically 'legal tender', but it doesn't mean that anyone has to accept it.

Of course, if you choose to take pound coins instead, bear in mind you'll only have until 15 October this year to spend them, before they are withdrawn too.