But Border Force staff at Heathrow felt a "zero tolerance" approach could "alienate members of the travelling public, leading to more confrontations", according to a report from the Independent Chief Inspector of Borders and Immigration.
An inspection team observing the green "nothing to declare" channel for those arriving from outside the EU witnessed "discretion" being exercised in two cases.
In one the passenger was marginally over the alcohol limit and was allowed to proceed.
In the other instance two women were found to be carrying excess cigarettes and tobacco. "One of them was elderly, and they were allowed to move into the red channel and pay the duty on the excess goods," the report said.
People arriving from outside the EU are allowed a certain amount of goods without paying duty or tax. Allowances include 16 litres of beer, 4 litres of wine and 200 cigarettes.
Instructions to staff state that when a passenger is intercepted arriving from a non-EU country and is found to be carrying undeclared alcohol or tobacco goods in excess of their duty free allowance, they must "seize all of the goods of the same type as the excess irrespective of volume or quantity".
Inspectors found that all of the Border Force managers and staff interviewed were aware that it was unlawful to exercise discretion in the area.
However, some felt there were circumstances in which it would be appropriate to do so - such as where a passenger held amounts "marginally" over the allowance or where elderly or vulnerable travellers were encountered with goods in excess of allowances.
Chief Inspector David Bolt's report said: "Officers stated that they were told by managers to target large seizures, and were afraid of becoming tied up dealing with low-level seizures and missing high-risk passengers or flights.
"They said that the paperwork involved in a seizure of 200 cigarettes was the same as for a seizure of 200,000 cigarettes. Some managers and staff questioned the cost effectiveness of making smaller seizures."
In group interviews most managers and staff said they should be allowed to exercise discretion when discharging their powers. Comparisons were made with police who do not serve speeding notices for driving at 31mph in a 30mph zone, the report said.
It concluded: "Border Force senior management had moved to ensure that officers in the customs channel complied with the law.
"However, the 'zero tolerance' approach was not supported in principle by some of those working in the channels, and not applied in practice in all cases."
Overall, the inspection found that the Home Office had acted upon recommendations made in a previous report on Heathrow.
Mr Bolt said: "I am pleased that standards in Border Force's operations were raised as a result of the recommendations this inspectorate made in 2015. But some areas require further attention and senior managers will need to do more to achieve the necessary improvements. "
In Taiwan, a traveller thought he'd come up with an innovative method of smuggling gold into Korea - by shaping it into clothes hangers. Unfortunately for the gold smuggler the idea wasn't smart enough as customs officers arrested him at Incheon International Airport with £52,000 worth of the metal. That's a lot of hangers...
In Bangladesh, customs officials seized 415 turtles from two men in Shahjalal International Airport. The mini reptile haul included 300 rare starred tortoises, 90 three-keeled turtles and 25 Indian roofed turtles. The animals were carried in three suitcases and worth an estimated three million taka (£24,760) on the black market.
Swiss border guards arrested six French citizens at Geneva railway station who were carrying more than 42 tasers disguised as mobile phones and flashlights, hoods, masks and laser devices. The strange assortment of items also included a cigarette lighter that hid a knife inside, an expandable spring baton, handcuffs and several balaclavas. Weird!
Some people are prepared to go to extreme lengths to commit a crime. A Chilean man travelling to Barcelona was found wearing a cast made from cocaine on his broken leg. Before he could claim the doctor had got the plaster mix wrong, airport security officers found bags of cocaine in his luggage too. It turned out he did have a broken leg but officials were almost certain he'd broken it on purpose to smuggle the drugs.
Customs officers at Melbourne International Airport discovered 51 live tropical fish concealed beneath the skirt of a female passenger. They selected a 43-year-old woman for a baggage examination after she arrived on a flight from Singapore and became suspicious during the search when they heard 'flipping' noises coming from her waist. An examination revealed 15 plastic water-filled bags holding fish in a purpose-built apron.
A Cypriot monk and two accomplices were caught trying to board a plane in Athens with the skull and bones of a nun in their luggage. When questioned about the remains in his luggage, the 42-year-old monk said he was transferring them from Greece to a monastery in Cyprus because the nun was a saint. But the Cypriot Orthodox church did not believe the story and said the attempted smuggling was sacrilegious.
A New York City man's attempt to smuggle a date rape drug into the US was sniffed out by customs dogs. The 50-year-old put the liquid in bottles and said it was "holy water" but lab tests confirmed the dozens of bottles contained Ketamine, a hallucinogenic used as a date rape drug.
An African prince tried to smuggle cocaine concealed inside onions into the UK. The 55-year-old prince thought the onion odour would hide the drugs worth £163,000. Shrimps and other smelly fish were packed in his luggage but sniffer dogs at Heathrow still managed to smell through the pungent odours.
Yuk! A smuggler was caught trying to hide a live Loris monkey in his underwear at India's Indira Gandhi International Airport. The little monkey measured seven inches in length and weighed 150g. Customs officers found it in his underwear while frisking him. Loris monkeys are an endangered species indigenous to South East Asia and India, and are believed to possess aphrodisiac qualities.
A woman and her daughter were arrested at Liverpool's John Lennon Airport in 2010 when they tried to check in the woman's dead husband on a flight to Berlin. They said the 91-year-old deceased man in the wheelchair was asleep but security was alerted when a member of staff became suspicious.
A woman in Barcelona was caught allegedly smuggling cocaine inside her breasts. Border police noticed the suspicious activity when the Panamanian woman arrived on a flight from Colombia with scars and blood-stained gauze wrapped around her chest. She was taken to a hospital and doctors found cocaine packed inside the implants.
A 48-year-old man tried to smuggle 14 rare Peregrine falcon eggs out of Birmingham Airport. Jeffrey Paul Lendrum wrapped the eggs in socks and attached them to his body to keep warm so that he could hatch them later. The eggs were worth £70,000 and were to be sold by the businessman in Dubai, where breeders will pay thousands of pounds for eggs snatched from the wild.
When customs officers at Kiev airport asked a Ukrainian woman to open her suitcase in 2007, they found a vibrator with a bag of hashish stuffed in the battery compartment. A border police spokesman said: "She told us that she had put the drugs in a vibrator because she thought no one would ever think of touching it, let alone looking inside it. She was obviously unaware of how thorough our officers are in their searches."
A 21-year-old woman declared a few soiled nappies at a US-Mexico border crossing but the suspiciously chunky diapers were seized when they were found to contain several links of spicy pork sausage. Customs officials said the nappies were folded to look soiled. Strange!
A man in Bangkok was caught carrying suitcases full of baby leopards, panthers, monkeys and a bear. The traveller thought he could smuggle the 'zoo' of animals through Suvarnabhumi International Airport for a flight to Dubai but undercover police had been watching him ever since he made the black market purchase of animals.
A Mr Potato head toy containing 293grams of ecstasy from Ireland was seized by Australian Customs back in 2007.