Shortly before Christmas a couple of years ago, I approached the check-in desk at a Spanish airport. Because my luggage had been misrouted on the outbound trip, obliging me to buy new clothes, I had an extra bag, and was preparing to pay to check it in. Just as I reached the desk a colleague phoned. Distracted, I handed over my documents – and found myself clutching the boarding pass, even though I was plainly breaching the rules on cabin baggage. But as the second bag went through the X-ray machine, I remembered I had a bottle of wine that would now surely be confiscated.

"What's that?" asked the supervisor, gesturing at the bottle-shaped object on his screen.

"It's a bottle of wine, and it's yours, Señor."

Instead of rummaging through the bag and removing the offending item, he waved me, and it, through.

Later, I raised a glass to his health – and that of airline passengers – thankful that common sense had temporarily prevailed.

Aviation security depends, we are told, on screening of every passenger and the removal of any object, from knitting needles to over-large tubes of toothpaste, that could conceivably be used in terrorism. We are assured that intelligence agencies are working quietly behind the scenes to identify and confound our enemies. But, to use the menacing mantra of the IRA, terrorists need to be lucky only once; we need to be lucky all the time.

The price of freedom to travel is eternal vigilance and – if you are male and flying to the US any time soon – experiencing what for many of us is unusual and discomfiting: a stranger stroking your buttocks while simultaneously rubbing his forearm against your groin.

As it happens, that is a technique I mastered many years ago while working in security at Gatwick, when such "pat-down" searches were conducted only on passengers travelling to Tel Aviv and Belfast, the flights regarded as requiring special scrutiny.

As from Boxing Day, the 25,000 passengers who fly from the UK to the US on the average day are all regarded as sufficiently suspicious to warrant such intrusive scrutiny. Furthermore, they can be trusted only with one piece of hand luggage, which must be searched twice before they are allowed on board a transatlantic jet. And, like sinful schoolchildren, they must sit still, strapped in and with nothing covering their laps, for the final hour of each flight. Such is the effect of the feeble and inept attempt to murder nearly 300 people on Northwest Airlines flight 253.

We are connected with America by more than just the best air links, and the "special relationship". We are also allied in military terms, which turns UK-US flights into trophies in the mangled morality of some terrorists.

After the Lockerbie bombing, 21 years ago last week, airlines started to match the passenger manifest with checked-in baggage. After 9/11, the American authorities started to take a much tougher attitude to both airport security and passenger background. Soon afterwards the British "shoe bomber" Richard Reid was apprehended, and consequently passengers often have to remove their footwear. And after the "liquid bomb plot" in 2006, a limit of 100ml on everything from shampoo to champagne was imposed.

Whatever extra hurdles are introduced permanently after the Christmas Day attack, they will suffer from the same intellectual flaw as all the existing formalities: they are pointless for the 99.999 per cent of passengers who hold no evil intent in their hearts and simply want to fly safely on holiday, business or a family visit.

Remove 100 per cent screening, say the authorities, and you open opportunities for terrorists. Yet the suspect who flew from Lagos via Amsterdam to Detroit breezed through the checks. Prospective terrorists would face far greater uncertainty if some flights were dispatched with a minimum of screening, while others received the full El Al treatment. And talking of the Israeli national airline: it has evaded terrorist attacks by assiduously "profiling" every passenger, looking at background and behaviour to identify prospective threats.

Plenty of young men of Middle Eastern, African and Asian appearance will say that they are already unofficially profiled, and they are understandably alarmed at encountering suspicion on grounds of skin colour, religion and national origin. But for profiling to be effective it must cast its net more widely, for example regarding travel journalists with distrust due to the propensity to travel alone, often at short notice, in the interests of "research".

Questions will be asked in Washington about how someone on an American "watch list" was allowed to board a US-bound flight – yet there have been plenty of false alarms involving British travellers, such as diverting a flight to Washington because it was carrying the peace campaigner Yusuf Islam (formerly Cat Stevens).

Britain has its recent past to blame for being firmly in the terrorists' sights. We are a nation constantly looking over our shoulder. But when I glance behind me, I would prefer to find an inquiring official asking intelligent questions rather than a strange man caressing my bottom.

New security measures

The revised security measures for flights into the US

*At departure: must arrive early, extra bag checks, and vigorous body pat-down searches.

*Strict enforcement of limit on one item of hand luggage.

*Wrapped presents in hand luggage must be unwrapped at the gate.

*During last hour before landing in the US: no access to bathroom, no moving from seat, no access to hand luggage, no items (including blankets) on lap.

*Some passengers travelling into the US have seen bans on the use of electronic equipment, including laptops and MP3 players.