The Price Marking Order 2004 has been a boon and a blessing to us all. Since it passed into law (thanks to the EU) it has not been necessary to carry a calculator on shopping trips to work out whether a 450gm jar of jam on sale for £2.37 is or is not a better buy than a 385gm jar of jam on sale for £1.99.

Now the unit price must be displayed making comparison a piece of cake, though sometimes (and perhaps in contravention of the regulations) one sees a price per 100gm against one product and a price per kilogram against a similar product. The unwary or those unable to multiply/divide by 10 can get burnt.

I reflected on this as I shopped for coffee today. Amongst the brands on offer was one in a 250gm pack at £3.53. That's a unit price of £1.41 per 100gm.

For those who find it tedious or challenging to measure out their coffee the same brand's range also included packs containing three sachets of what they described as microground and instant coffee at £1.45. Of course you have to pay for the convenience of being able to rip open a sachet and empty the contents into your cup instead of going through all that messy and potentially inaccurate spooning.

Thanks to the Price Marking Order 2004 you can see how high a premium that convenience carries because coffee bought in this packaging costs £21.02 per 100gm. To be fair it's not exactly the same coffee in both cases but it would have to be some super duper coffee to warrant a price multiple of nearly 15.

Putting it another way, and I confess to using a calculator to work this out, the convenience premium per cup is about 40p. The inconvenience premium of having all that packaging to dispose of is incalculable both for the consumer and the planet.