TELEPHONE Coca-Cola and, while you wait to be put through, the corporation's 'It's the Real Thing' jingle crackles down the line. 'It's the Real Thing' is a global message first used by Coca- Cola in the Forties; its meaning is clear (do not be fooled by lesser imitators) and it is inescapable. It translates perfectly well into Roman, Arabic, Cyrillic script and most other languages and stands for an instantly recognisable product in Birmingham (Alabama), Birmingham (England), Bali or Bangkok.

This is the advertising technique now being taken up by more and more companies and advertising agencies from British Airways to Benetton as their products reach out around the world. Huge resources are being poured into single advertising campaigns: the recent wave of BA advertisements features casts of thousands - literally.

The idea behind the advertising is that we really are part of some global village: we all want the same things, we all have access to them and we all respond to the same imagery. Coca-Cola sells itself as democratic, international and liberating; no wonder it's good for you.

The sub-text might be that corporations such as Coca-Cola and BA want to be seen as worldly, altruistic giants, linking the peoples of the world in one warm and smiling embrace - all the better to sell them things. An added bonus for the company is that they only need their advertising agencies to produce one idea, rather than one for every country. This means the advertisement itself can be more spectacular, without the campaign necessarily being more expensive.

The latest BA adverts read exactly this way, as did the 'United Colours of Benetton' ads in their less controversial days - when, rather than seabirds smothered in oil or young men dying of Aids, their striking images depicted children of different colours wearing different coloured jumpers.

Coca-Cola was the first company to break into global advertising. The most memorable of these early international adverts was 'I'd like to teach the world to sing . . . Coca-Cola . . . the real thing', made in 1971 and reshot in 1989. The ad featured a crowd of young people, ostensibly from all corners of the Earth, learning to sing the words 'Coca-Cola' in perfect harmony while smiling through even more perfect white teeth.

Coca-Cola has been conquering the world ever since GIs took it with them along with Uncle Sam to Europe, South- east Asia, South America and the Middle East. By sticking to its guns and making just one key, desirable and homogeneous product, Coca-Cola's advertising agencies have been able to promote the drink with messages so simple that they can be posted around the world without causing confusion, upset or censure.

Simplicity is the key; they are easy to understand, easy to translate and, after being repeated enough times, become synonymous with the product. Can they become more sophisticated and be equally successful?

John Bartle is one of the creative partners of Bartle Bogle Hegarty, the agency that devised the famous 'Vorsprung durch Technik' campaign for Audi, and Levi 501 ads since 1982 (Nick Kamen stepping out of his jeans in the launderette, 'There's rivets and there's Levi rivets', and the current one in which a latter day Princess Charming gets men to try on a pair of dropped 501s until she finds her hunky Cinderellus).

According to Mr Bartle, 'The most effective global ads are those with the most powerful image: trying to appeal to hundreds of millions of people from different cultures doesn't mean that you have to set out to appeal to the lowest common denominator. In fact, quite the opposite is true. Our Levi ads have been shown worldwide and our Haagen-Dazs ice- cream ads will travel a lot further than just Britain and Sweden as the company expands.

'The best global adverts of all are the ones that start with a strong message in their home market - as Marlborough and Coca-Cola did - and then export the same message around the world.'

Even then, the simplest ads can go wrong, and cause offence in one country when they are considered perfectly chaste in another. It is unlikely that the raunchy Haagen-Dazs campaign, for example, would go down well in Tehran. 'We once did some work for Pepsi,' says Mr Bartle. 'One of the things I most remember was the long list of dos and don'ts applying to campaigns in the Middle East and Muslim countries.' Like what? 'The role of women is always an area of concern; but to show someone holding a can of drink in the wrong hand (Muslims think infidels disgusting for eating with the same hand that wipes their bottom) could destroy a product like Pepsi or Coke overnight.' Coca-Cola advertises in most countries in the world: one of the only exceptions is Iraq - yet not, apparently, because of Saddam Hussein.

'In the Nineties,' says Marcus Ritch of McCann Erikkson, 'Coca-Cola is beginning to develop more local ads working on the 'think globally, act locally' principle, although 90 per cent of its advertising will continue to be generated in the United States.' Is it possible to develop convincing local ads without a product losing a global identity?

'That's exactly what we did with the 'Vorsprung durch Technik' campaign for Audi,' says Mr Bartle. The cars advertised were global products with little character either innate or overt. What might appeal to a car buyer around the world is the Audi's solid engineering.

'Our ads played on a very British view of the assumed German obsession with technology. In this case, it seemed better to build up the local market rather than going for a sweeping, global approach. In any case, Audi was hardly as well recognised in Britain as Coca-Cola; most people couldn't even pronounce the name.' If the make had been well known, the adverts might have been less entertaining and probably - although there can be no proof - less successful.

What matters in the end is the product. Advertising can sell a product to the world if the world likes it and goes back to buy it again and again. As BA has found to its cost in recent weeks, global advertising slogans can backfire when the product turns out to be something less than 'the world's favourite airline'.

(Photographs omitted)