When it comes to disruption, false alarms do the work of terrorists

The Metropolitan Police are very clear in a new poster campaign in the capital. "Terrorism won't succeed if someone reports suspicious bags, vehicles or behaviour: You are that someone." On the contrary: false alarms can do the work of terrorists in disrupting life for Londoners and tourists.

Following the suicide-bomb attacks in July that tore so many lives apart, the scope for upheaval has intensified. I was aboard a South Eastern train, heading from Kent to the capital, that stopped suddenly outside London Bridge station, where many lines converge. The entire network came to a standstill. After half an hour, it became clear that our train had been isolated because of a bomb threat. A group of youths at a station down the line had spotted a dark-skinned gentleman with a rucksack boarding the train. They had reported him as a suspected suicide- bomber. So the train was isolated and all other services halted while London Bridge station, one of the busiest in the capital, was cleared of passengers and staff.

Eventually, our sealed train was allowed to proceed to the station, where the welcoming committee comprised a dozen police and two dogs. They kept the train's doors locked while they went through the carriages and discovered the nature of the supposed "threat". As a result of what was quite possibly a mischievous report, thousands of people had their travel plans ruined. London Bridge is the midway point on the rail link between Luton and Gatwick airports, and many passengers missed their planes as train after train was cancelled. And I fear that some foreign visitors will have decided to holiday somewhere else next time.

The police are obliged to take seriously reports of "suspicious bags, vehicles or behaviour", but the contention that this will defeat terrorism is seriously flawed. As is the barmy idea of installing an optional security check at Paddington station for passengers taking the Heathrow Express. Travellers on the fast link to our busiest airport are invited to subject themselves to intimate security screening; anyone in a hurry, or with evil intentions, can simply decline.

GERMAN RAILWAYS has problems of a more mundane nature. The German language has some good words for travel-related concepts: wanderlust, the desire to travel; mitfahrer, to share a ride; and schwarzfahrer, literally, to travel black, the term used for fare-dodging.

By the end of next year, ticketless travel should be universal for air passengers - the International Air Transport Association (Iata) aims to scrap all paper tickets in favour of the electronic version. But on some parts of the German rail network, as I reported last month, ticketless travel seems to be the norm. Following defeat at the hands of fiendish ticket-issuing technology at stations in Germany, I boarded a train without a ticket. As I discovered when inspectors boarded the train, so had practically everyone else.

Judging from the flood of correspondence on the subject, my misdemeanour was far from unique. A translator living in Germany, Moya Irvine, says: "Everyone complains about those ticket machines. They are designed so that if the sun shines on the screen, it's impossible to read what's on it. I've seen little old ladies marched off the train for not being able to cope with the machines."

I asked Ms Irvine for the German equivalent to "it's a fair cop, gov"; it is jetzt hat's mich halt erwischt, which means, literally, "it has caught me". In the past, it has caught a senior figure in the travel industry. The executive, whose identity cannot be revealed, writes in with a confession about being apprehended by a couple of plain-clothed inspectors: "I burst into knowing and shameful laughter when I read your piece on schwarzfahrer. As a law-abiding teenager, I travelled on Frankfurt buses to school and always paid - until one day I forgot. I was promptly caught by two little old ladies, handbags at the ready, in a pincer movement from both exit doors."

The writer paid up; the penalty then was only 20 marks (about £6), compared with the current €40 (£28). But she got her money back: "Being a poor student, I had to make up for this and spent the ensuing years not paying when returning from Saturday nights on the tiles."