Thankfully, help is at hand. Time Out, London's listings guide, has made provision for that very occasion. As their new classified column "Once seen... Never forgotten" says, "Glances across a crowded carriage, then the doors open and you'll ever meet again... Or will you?" For a legion of lovelorn Londoners it represents another bite at the cherry, and after only a month in existence, it's already a success. Once Seen is brimming with clear-cut hopefuls like: "Piccadilly Line, 7th Feb, 7:25am. Blond man, dark green eyes, light chinos. Please make contact again with blonde woman travelling with German couple, getting off at Green Park." And "Camden Town station. I see you most mornings, 10-10:30. Long wavy brown hair, 6ft-ish, light brown jacket and glasses. You have a great smile. Fancy a coffee one morning?" Could this be the end of the chat-up line as we know it?
Once Seen differs from other introduction services in that, loosely defined, those who advertise and respond have already met. Nigel Tradewell, who runs the section, explains, "The Underground's a difficult environment to make contact in. Everyone's missed their chances; it's easy to think 'I should have asked her'. Even though people are hiding behind their papers, making a pass doesn't exactly go unnoticed by the rest of the passengers. We're trying to make it all a bit more fun and imaginative."
With the bulk of Britain's singles population based in the South East, the sustained gaze is part and parcel of the Underground. But what if you should seize that moment of romantic opportunity? Pauline Rennie-Peyton, a psychiatrist specialising in relationships, is resolutely sceptical. "Sorry to sound so middle-aged, but the most solid relationships are based on friendship, and often in these cases it's all down to sexual attraction." If you're determined to go for it, "You must be confident and be prepared for rejection." If you're subject to another person's play, Pauline advises caution. "These situations can be very dangerous for women. Meet them for coffee or lunch but don't give an address or phone number."
Still, sometimes it pays to be a little reckless. Ed and Camilla bear witness to that. Ed was travelling back from his first day at a London ad agency in 1988 when he spotted Camilla on a District Line train. He recognised her from his former university, but they were otherwise unacquainted. "The Tube was pretty crowded but I was oblivious," Ed says. "Camilla was seated and I deliberately stood in front of her. I conjured up the courage and came out with the immortal line 'Weren't you at Durham?'" It was a bold move but Camilla responded and they got chatting. He continues: "We changed at Earl's Court, a brilliant station for romance because it's so confusing. Although we parted company without exchanging numbers, Camilla had gone the wrong way, so when she suddenly reappeared we had a few more minutes together. Her train was coming and, when I asked for her phone number - I'm not making this up - she actually passed it through the closing doors." They married three years later. Now that's a love story.
"Life's full of risks," says Drusilla Beyfus, author of Modern Manners, "and nobody's immune to Cupid's advances, but there are many taboos about making advances in public. It's best to act on your instincts." Beyfus recommends planning a liaison and preferably incorporating friends to see how it works. She emphasises that "the girl should always take along a third party for safety".
For, naturally, the creep-factor lurks in the shadows of any such situation, and the Tube certainly has its quota of weirdos. Even the classifieds have their uncertainties; the usually cheery Once Seen contains the vaguely weird entry "I saw you once, you were female, mid-twenties, I knew you were my soul-mate." So, before blitzing a likely inamorata with your advances, it's important to remember that it could earn a hostile reception.
Jayne's first encounter with her boyfriend, Tim, on a late-night tube from Bond Street, was anything but a fairy-tale beginning. Tim, a writer, recalls that special night. "It was the last tube on a Wednesday in late November. I distinctly remember looking at the clock - it was 00:08 and I was reading the Penguin History Of Greek Philosophy. Then Jayne got on. I'd seen her once before in a cafe in Soho and as she walked towards me she was kind of looking at me, and at the same time kind of looking straight through me. I said hello and was blanked."
"Normally, I don't look at anybody," Jayne says, "but I made eye-contact by mistake. Tim saw I was getting nervous and tried to put me at ease. I was so relieved when he broke the ice." Tim continues: "I explained where I'd seen her before and we started talking." It transpired that they lived a couple of blocks apart. "I didn't want to push for her number,"says Tim, "so I said I'd be in that same cafe the next night. Jayne showed up."
So, where's the most romantic place to start looking? "The District Line has the edge," says the London Tourist Board. "From Earl's Court to Richmond it goes overground past Kew Gardens. Or Putney to Wimbledon. Earl's Court and Camden are like pick-up joints, especially at weekends. As for the sexiest station, Angel gets the vote. Maybe it's due to that gigantic escalator." With a name like Angel, how can it fail?
Maintain eye contact. Remove sunglasses but keep your hands to yourself
Offering a seat is definitely a good move, despite being seen as an act of weakness by other passengers
Props are useful. A book is indicative of personality, but Proust could mean different things to different people
Alcohol may inspire courage, but remember the last tube is used by others, and drooling is unsightly
If you do get lucky, exercise some restraint - there is a
hungry market for CCTV