It is always so tempting. There's a till free, there are only a few items in your basket. How difficult can it be? The decision is made and you're there, face to face with the supermarket's self-service check-out till.
But for many people, this simple decision often turns out to be a source of such frustration that it ruins the rest of their day, leaving a lasting sense of resentment and ineptitude.
Supermarkets championed the introduction of self-service tills as a means of reducing queuing but, with a twist of irony, research now shows that for some customers they have had the opposite effect and actually increase waiting times.
What's more, supermarket staff who bear the brunt of customer exasperation at the failings of the new checkout technology have reported a new phenomenon: self-service till rage.
This unexpected anger in the bagging area is usually prompted by frustrations at the behaviour of the machine, even if the glitches are really down to the customer's cack-handedness. The eggs won't scan, the machine can't identify the turnip on the till, and the bar codes on every item in the basket are hiding in the most obscure part of the packaging.
Swiping items across the scanner in quick succession seems unacceptable to the machine and a member of staff has to be summoned to verify you're old enough to buy alcohol. Perhaps most annoying of all is the robotic call of "Unexpected item in bagging area", which rivals "Your call is important to us, please hold" as a blood pressure-inducing curse of the automated age.
A survey carried out by the shop workers' union Usdaw has, for the first time, identified self-service till rage as a cause of abuse. John Hannett, the general secretary, said that as yet, it accounts for only 3 per cent of cases but that it is an alarming source.
"Our concern is that the use of self-service checkouts has become a flash point that can lead to abuse and violence against shop workers," he is reported as saying. "Frustrated shoppers experiencing problems using self-service checkouts can often take out their anger and frustration on the nearest shop worker, and this is unfair and unacceptable.
"We will be very concerned if the situation worsens as the use of self-service checkouts becomes more widespread. On the whole, shoppers much prefer to be served by real people."
Self-service tills were introduced in 2002 and they are now found in most supermarkets. By next year, there are forecast to be 15,000 in use in Britain. The units take up less space than the traditional manned conveyor-belt type, so more can be installed, but supermarkets insist that their introduction is not merely a simple means of reducing staff levels.
Freeing staff from the need to man a till gives them more time to replenish shelves, according to the supermarkets, which are acutely aware that when a customer cannot find an item they may well leave the building without buying any of the other products they might have wanted.
Research by The Grocer magazine concluded that average waiting times at Tesco and Sainsbury's, the stores with the most self-service tills, have increased on tills operated by a member of staff. The average wait on manned tills at Tesco rose from 5 minutes, 15 seconds to 5 minutes, 45 seconds since 2008. For Sainsbury's, average waits rose by five seconds from 5 minutes, 30 seconds.
The magazine did, however, find that Asda and Morrisons checkout times had been improved by the introduction of self-service tills. Supermarkets were dismissive yesterday of suggestions that the tills were unpopular, although an Asda spokeswoman conceded that customers still preferred to use the manned tills. "Most people prefer still to use the normal checkouts," she said.
At Tesco, which now has 6,000 self-service tills across its 1,200 stores, a spokeswoman insisted that the technology was popular among customers.
"We continually get really good feedback on them from customers," she said. "Many customers actually prefer using our self-service checkouts as it's sometimes the quickest way to pay, particularly if you only have a few items.
At Sainsbury's the self-service tills are part of investments being made by the store chain, a spokesman said, to cut the time a customer takes to check out by 12 per cent.
NCR, formerly the National Cash Register company, makes four-fifths of the self-service tills installed in British stores and regards their introduction as the biggest innovation in shopping since the 1950s. "When Sainsbury's launched its first self-service store, some customers said it would never catch on," a spokesman told The Sunday Telegraph.
"Now we expect grocery retailers to have tens of thousands of products available, which would be an infeasible number to provide over a counter to individual shoppers."
The woman's voice used by the self-service tills was chosen by the company on the grounds that it had "a calm and approachable" manner. An M&S spokesman denied the tills had been a cause of checkout rage and said the self-service units have been welcomed by customers.
"Our customers currently make over 600,000 transactions a week using these tills," he said. "Wherever there are self-service tills present, customers always have the option of using a manned till point."
NOW IT'S THE DRIVE-THRU SUPERMARKET...
*Not content with its self-service checkouts and internet ordering service, Tesco yesterday announced its intention to open the UK's first "drive-thru" supermarket in a fresh attempt to woo Britain's busy shoppers.
The service is aimed at customers who do not want to carry out their weekly shop themselves, but also do not have time to wait at home for an internet delivery.
Instead, for a flat fee of £2, they will be able to drive to a dedicated area in a Tesco store at a set time and pick up their shopping without having to leave their car. However, the service is only £1 less than the cheapest option for having shopping delivered to your house through Tesco's website – a fact sure to raise the eyebrows of the country's more cynical consumers.
A pilot drive-thru is being launched at Tesco Extra store in Baldock, Hertfordshire, today. If it is successful, the group plans to roll it out across other areas of the country, but does not have a timescale for the expansion.