It's one of the most famous tunes in cinema history and one guaranteed to get people singing along - even though it's nothing to do with the actual films

THE lights in the auditorium dim. As the curtains part, you settle back in your seat clutching a Kia-Ora drink in one hand and a bag of Butterkist popcorn in the other. Then the oh-so-familiar music starts... pa-pah pa-pah pa-pah pa-pah pa pa pa.

The name Pearl & Dean that goes with this most famous of musical pieces is pretty well-known too. For 50 years this has been one of the biggest names in cinema advertising. Just like the main feature that follows the commercials, its story is one of triumph and tragedy, success and failure - with a theme tune that may not have won any Oscars but is a lot more hummable than many award-winning scores.

Movie stars have come and gone, tatty fleapits have been replaced by multiplex cinemas, and slide show adverts for local Indian restaurants have been replaced by big budget mini-movies for top brand names. Even Kia-Ora and Butterkist have been replaced by giant buckets of popcorn and cola. But Pearl & Dean goes on forever, entering its half-century with just under a 40 per cent share of the cinema advertising market.

It all began with Ernie and Charles Pearl, travelling salesmen who sold simple slide advertising and commercials to local businesses in the 1930s for a company based in Cardiff. Their big break came in 1953 when they joined Bob Dean in setting up Pearl & Dean to represent the ABC cinema circuit as its main contractor.

The company's debut coincided with a change in cinema ads, prompted by the growth of commercial television in that decade. Traditionally, movie house ads were quite long. Soon Pearl & Dean were showing shorter, snappier commercials for leading brands, such as Unilever and Beechams.

Before long, it was the UK's leading cinema advertising contractor, at one point holding 65 per cent of the UK cinema market as well as operating in the Far East. Then, during the early 1970s, Messrs Pearl and Dean sold their stakes in the company - a move that coincided with a sharp fall in cinema audiences, which had yet to fight back against the competition of TV.

This was a bad time for Pearl & Dean. The new owners, Mills & Allen, was a poster contractor with little experience of the moving picture industry. Rank Screen Advertising moved to the fore and snatched the ABC/Cannon contract in the mid-1980s. The pa-pa pa-pa lost much of its pa as Pearl & Dean's market share slumped to a lowly 12 per cent over the next decade.

The future was looking as bright as Hollywood star's career after three flops in a row. Help came in 1993 when a group of French media interests, led by Havas and Mediavision, purchased the company for a nominal sum and then successfully re-launched Pearl & Dean under new management.

Six years later, Scottish-based SMG plc bought the company. It has now regained a significant market share, being the sole screen advertisting contractor for Warner Village, UGC, Apollo and SBC cinema circuits. It also markets screen time in more than 120 independent cinemas in the UK and two UCI multiplexes.

With admissions at their highest levels for over 30 years, cinema commercials have come back into their own. When blockbusters like the Harry Potter movies are screened, the number of commercials showing before the main film can more than double.

Cinema advertising is attractive because cinemas can reach audiences other advertising media can't - the elusive 16 to 25 age group, which has money to spend but doesn't watch a lot of telly. Movie houses are able to target audiences more easily, although the amount spent in cinemas is still tiny compared to the vast sums handed over by advertisers to promote their wares on TV.

Long after people have forgotten the product, they're still pa-pa-pa-ing Pearl & Dean's signature tune - or Asteroid, to give the 20-second tune its proper name. It's reckoned that some six billion cinemagoers have heard it over the years.

The man who wrote it was composer and arranger Pete Moore, who worked with many famous singers in the 1950s and 1960s including Bing Crosby, Fred Astaire, Gene Kelly, Peggy Lee, Frankie Laine and Connie Francis.

When the time came in the early 1990s to give the tune the full stereo treatment, Moore was able to track down two of the three original male singers to replicate their vocal parts three decades on. Then Goldbug, fronted by ex-Beastmasters' Richard Walmsley, sampled the Pearl & Dean theme and made number two in the singles chart with Whole Lotta Love in 1995.

"When I wrote Asteroid, many people in the profession accused me of writing music for the future, and ahead of its time. With the longevity of this music, I thoroughly agree," Moore noted two years ago.

To coincide with its 50th anniversary, Pearl & Dean has launched a fund-raising initiative in aid of two charites, the Children's Hospice Association of Scotland (CHAS) and MediCinema, which installs cinemas in hospitals for patients.

And, of course, they're promoting the charities with cinema commercials. Actor Ewan McGregor, a patron of both charities, wrote and directed the cinema appeal for CHAS, and provided a voiceover in the MediCinema appeal. The latter was written by John Hodge, who scripted the films Trainspotting and Shallow Grave.

Asteroid won't be forgotten, celebrated in an anniversary musical button badge. All profits from those and a specially-designed T-shirt will go to the two charities.