It seemed to be one of EastEnders's finest moments, but it may instead have been the first ring of its death knell. Some 17 million people watched Dirty Den return from the dead. Fourteen years after his bullet-ridden body had dropped into the canal, he was back and the soap opera looked in fine health too, writes Shane Hegarty

But one year on, EastEnders is in serious trouble. Its executive producer has been sacked, many of its stars face the axe and it's getting trounced in the ratings. In Britain and in Ireland, viewers are turning off. One recent episode was watched by only 6.2 million in the UK, its lowest ever rating.

Next year, the drama will celebrate its 20th birthday. Speculation that it will not survive far beyond that is probably premature, but the ghost of Brookside is still rattling its chains. Channel 4's soap once had both high reputations and a reputation. During the Thatcher years it was nakedly political, and yet it pushed the boundaries of what stories soap could get away with. It had incest, murder and a lesbian kiss. It had a successful balance between sensationalism and everyday concerns.

Gradually, though, the other soaps began to follow its lead and it was pushed off its perch. It became increasingly outlandish in the pursuit of killer storylines. There were cults and helicopter disasters. But by then Coronation Street had introduced a transsexual and a serial killer.

Brookside's ratings slid, until the show was axed. The question is no longer what will come along to replace it, but which soap will be next to go.

It's a crowded market and the pressure for bigger, brasher storylines is obvious. Last week, TG4's soap Ros na Rún featured scenes in which a mother jumped to her death from a pier while holding her baby son. It was the culmination of a long-running story that involved adultery, rape, a car crash and a coma. The story was used for a big push by the soap, with trailers running on RTE for some time in advance. Yet, in a country where you might have thought that the collision of suicide, motherhood and infanticide would ruffle some feathers, TG4's switchboard remained quite untroubled.

Viewers are used to bombastic storylines. The fear is that they might become immune to them. "You don't want to push it too far too often," says Ros na Rún's producer, Trevor Ó Clochartaigh. "We try and take the long-term view, avoiding issue-driven drama and making sure it comes from the characters instead. A big story might give you a short-term gain, but if you are to be credible in the long term you have to build up the characters." Ros na Rún has to fill only two half-hour slots a week, and gets a summer break, meaning that it is under less pressure to churn out big stories. Fair City and EastEnders go out four nights a week. Emmerdale is on five nights. Some weeks Coronation Street delivers six episodes.

The pressure for fresh stories and characters is enormous and has certainly taken its toll on EastEnders, which has lost its humour and credibility as its characters have become gloomy under the toll of relentlessly grim and often absurd storylines. Many tribulations have been rained down upon its characters and it has had its characters do things that are implausible, such as Sonia marrying the killer of her first love. Meanwhile, the actress Jessie Wallace (Kat Slater) is obviously pregnant, but they have not written it into the plot. And while Dirty Den's return was a response to Coronation Street's success with Richard the Serial Killer, a similar story was derided when Bobby Ewing emerged from the shower in Dallas; the moment that marked the beginning of the end for that soap.

When a soap loses its credibility, it can be hard for it to get it back.

David Liddiment, a former executive producer of Coronation Street, argued recently that relentless, demanding schedules and intense competition are gnawing away at soap opera's roots, that they are in danger of reflecting the daily lives of its viewers less and less, and becoming more like the crazy US daytime soaps. "In terms of credibility and quality, the cracks are beginning to show, " he said. "If there is too much soap, its link with reality will be broken and then Coronation Street and EastEnders will go the way of Brookside." Fair City's executive producer, Niall Matthews, says success depends upon getting the balance right and not going too big too often. "There are different degrees. A child getting a belly piercing is minor in the great scheme of things, but it's a relevant story. Then you go all the way up to death, which is the highest stakes. EastEnders goes with the higher stakes, and when you keep pitching higher you almost have to outdo yourself. You run out. Where do you go after life and death? There is no place to go." He says people are always asking him when Fair City will bring its infamous gangster character Billy back from the dead. Even if his time saw enormous ratings, if he were to come back he'd only end up doing the same things again, says Matthews, so there's not much point in doing it.

Fair City's research had showed there were only two stories viewers wouldn't accept: paedophilia and incest. Yet both of these have been done - although in ways that, he says, reflected the research. The aftermath of paedophilia, rather than the act, was shown, while the incest story began as a love story between two people who didn't know they were related. It's how you handle a story that matters, he says, pointing to Fair City's abortion and breast cancer stories as examples of headline-grabbing plots he feels were treated sensitively.

Matthews doesn't agree that there are few stories left. "It's like saying that every article has been written. It isn't true. You have to think in terms of characters. Think in terms of the people in your office. They are all different. They all react differently to events." However, he's not sure if the soap could cope with another night a week, purely because of the strains it would put on all those behind the scenes.

"But there seems to be an unending appetite for soap," he adds. "When we went from two to three to four nights I couldn't believe it, but the appetite just seems to be there and people are able to go from one to the other easily."

"People will always want to see their own lives on stage or screen," believes Trevor Ó Clochartaigh. "There is always a role for that, whether soap becomes hackneyed or tired or not. It is possibly over-saturated at the moment. When I was growing up they were on for two nights or one night a week. There was a sense of occasion. Now they're on for four or five nights and there is that old danger of familiarity breeding contempt." Yet Coronation Street has had its crises in the past, but has come through strongly and is currently winning the ratings battle.

And soaps still get away with the most ridiculous things. When Emmerdale went from gentle rural soap to gritty rural drama in the early 1990s, it used a Lockerbie-style plane crash to weed the weak from the strong. From such an over-the-top point, however, the soap has gone from strength to strength. On the night EastEnders reached its lowest point, 8 million viewers watched an hour-long Emmerdale special that featured cancer, a cat-fight, a punch-up, a wedding and that soap staple, a secret son revealed.

Meanwhile, EastEnders's problems are not just in the scripts. Its actors have been making front-page headlines for scandals sometimes more outlandish than anything the scriptwriters could come up with. Most obviously was the revelation that Leslie Grantham (Dirty Den) had been performing sex acts in his dressingroom for the enjoyment of Internet voyeurs. When EastEnders becomes more interesting on screen than it does off, you'll know that the crisis has been averted.