Pour your heart out on the answering machine; send three dozen red roses on Valentine's Day; have a banner flown across the rooftops and he (or she) will think you romantic and extravagant. All a waste of time, unfortunately, if he (or she) also finds you totally physically revolting.

There comes an age in mating affairs when a sad fact has to be acknowledged: looks count. Beauty may be only skin deep but hell, where would we be without skin? Chiselled jaws are not everyone's idea of perfection, which is lucky for the 99 per cent whose bone structure hardly even makes an appearance, but even those who like treble chins know what they like.

On the fourth floor of a narrow building in narrow Villiers Street, near to Charing Cross station in London, the pictorial image is paramount. The Picture Dating Agency makes no bones about it, chiselled or otherwise. Its 2,000 clients, each searching for the perfect partner who has so far eluded them, flick through files that include the usual data - age, height, pathological hatred of smoking and fried liver - and the all-important photograph.

From behind her desk in the peach-coloured office Alison Jones, who has worked at the agency for three of its four years, concedes that many clients do not get beyond this, the photograph. In her experience, no other aural or intangible characteristic is as decisive. Why waste time? Those engaged on heart searching, she says with candour, grow sick of finding themselves falsely seduced by voices, most wicked deceivers, on the end of telephone wires.

'Voices don't go with looks,' says Mrs Jones. 'A lot of people who join us have placed ads in Time Out and say, 'they sounded wonderful, then we met . . .' ' Even Jeremy Wright, founder and partner of the agency, has fallen into the same trap. A woman he chatted to and chatted up over the telephone in his days as an advertising company's finance director should, he says, have remained merely a telecommunication fantasy. Instead, she became a shattered illusion.

Most people, if pushed, will admit that looks do matter, even if only for the first 10 seconds. In the 11th second the wit, vivacity and stupendous sense of humour take over but, it seems, in the rather strained business of intimate personal relationships it has to be in that order. Otherwise something fundamental and chemical occurs which has the definite but inexplicable effect of snuffing out all vestiges of passion.

So it may seem peculiar that of all the dating agencies trying to appeal to all the beautiful people in London, existing in a milieu of perfumed and worked-at loveliness, only a handful accept the importance of the visual first impression.

Across the Strand from Villiers Street, Maiden Lane is, coincidentally, the address of another. Natural Attraction goes one step further and makes a five-minute video of all its clients. For a special price of pounds 50 until Valentine's Day, members can give it a two-month trial and take advantage of the 'video library' of other members.

Kim Franklin, the charming American founder, does the films herself, leading her nervous subjects up to the fourth floor of pale yellow rooms and, to her credit, achieving a moderate degree of relaxation from them as they sit on the fuchsia pink leather settee and chat about themselves. Ms Franklin has brought the idea over from Los Angeles where video dating agencies are standard. She would have liked to join one herself after her divorce, she says, but could not afford the dollars 2,000 annual fee.

'Every single person has a nervous habit,' she says, watching one of her subjects fiddling with his cufflinks. 'It just shows you're human. This way, the gist of the person comes across; it's nice to hear somebody's laugh and voice and can completely change your perception of how a person looks. People are always surprised by models when they see them interviewed.'

She recalls her own experience of blind dating with a mild degree of horror, recalling the feeling of wasted time and emotion when she and the other party simply failed to gel. She met the man who was to be her husband through her mother; he was a close friend's son.

The Picture Dating Agency and Natural Attraction are somewhat disparaging about the other's chosen methods of visual dating. Mr Wright says clients feel much easier about sending in their own chosen photographs and (though it might be all right for extrovert Americans) would probably freeze when faced with a video camera. Ms Franklin asks how a still picture can possibly present the total visual impression a person gives, and points out that a good studio will issue a very good photograph (in fact, most of the pictures supplied are just snapshots or masochistically cruel mugshots that come out wet and insulting from station forecourt booths).

In the final analysis, though, both agencies share the view that no matchmaker can predict the chemistry that makes or breaks a first meeting, no matter how assiduous the matching process and how intuitive the matchmaker.

'I know lots of agencies who do psychological tests and charge pounds 2,000 for it,' says Mr Wright, whose fees are a modest pounds 130 a year for the 'gold service', which includes unlimited introductions and free access to all the files, plus notification when one's own file has been selected by another member. 'But really, it's when you meet and click that the process is successful.'

So far, at least 20 marriages have their roots in Villiers Street but unlike Cilla Black, who is invariably invited to all nuptials in which she has played a part, neither Mr Wright nor his business partner, Saphel Rose, has ever been a guest. Practicality may extend to photographs but the mild stigma of having met through an agency apparently lingers on.

Why should this be? Both Mr Wright and Ms Franklin point out, accurately, that forging romantic links in large cities is a harsh enterprise, consisting of screamed conversations in smoky wine bars or claustrophobic liaisons at work. Why should this business not be undertaken in a mature and sensible way? No one can answer that, but few will admit to joining a dating agency.

Jonathan, for example, a stunningly good-looking 37-year-old lawyer registered with the Picture Dating Agency, has no objection to his file being looked at, but would probably recoil in horror if his friends knew he had one. Indeed, his real name is not Jonathan at all.

Adam Black, however, is called Adam Black and is prepared to be recorded as living in north London and working as a film location manager and producer. He is registered with Natural Attraction, which put him on the other side of the camera.

'I meet a lot of people through work, but there's the rub,' he says. 'My friends in successful relationships have partners who do other jobs.' Physical attraction, he says, is vital in the formative hours of a relationship, and the last thing he wants to do is talk work. 'I want to talk about love, have good sex, eat wonderful food and have fun.'

Natural Attraction, he says, goes some way towards dispelling the entrenched attitude that agencies are not quite the right thing to do. So far the sex and food have eluded him but then again, his video is barely cold from the camera.

Natural Attraction, 17 Maiden Lane, London WC2E 7NA (071-379 6697).

The Picture Dating Agency, 29 Villiers Street, London WC2N 6ND

(071-839 8884).

(Photograph omitted)