Cockles in the Thames estuary are subject to rigorously enforced conservation schemes.

Cockle fishermen have no such luck.

Fishing has been run on a commercial basis in Leigh for at least 400 years. Now its days as an industry could be numbered.

The cockle beds of Leigh are under a two-pronged attack, from a sustained campaign to open up the beds to outsiders, and from the effects of new legislation.

The catalyst, of course, was the event which brought the word cockle, possibly for the first time, onto front page headlines.

"Who would ever have thought that this humble mollusc would become the focal point of a mass tragedy and international media story?" mused the BBC's Today programme presenter John Naughtie In reality, the cockle was never that humble. It was already big business, when, on February 5 2004, it turned into big politics.

On the night that 23 Chinese migrant workers drowned in Morecambe Bay, Lancashire, caught out by the bay's notorious riptides and quicksands, they were serving an industry worth an estimated £8million a year in Morecambe Bay alone.

The cockle beds off Leigh are just slightly less valuable, yielding around £7million per annum.

In a good year, the full British Isles quota is worth about £40million.

Most of the catch goes to Spain, for canning. Like many a human Southender, the tinned cockles on British supermarket shelves have been on a trip to the Spanish coast and back again.

The story of the Morecambe Bay tragedy forms the background to a new film, Ghosts, released in cinemas this month.

The film is not into fence-sitting.

Its view is that greed led directly to the tragedy.

It lays the blame directly at the door of the big supermarkets, the ultimate beneficiaries of cheap immigrant labour in the food industry.

Cockle money is blood money is the message. So now it's a movie star.

The cockle really has climbed up the political agenda.

Anger at the circumstances of Morecambe Bay have led to reactive legislation.

And fishermen in the Thames Estuary could be hit by the knock-on effects.

Yet a tragedy on such a scale could not have happened here.

The Chinese gangs practice traditional cockle harvesting, by hand, using a rake and sieve, a method unchanged in 10,000 years.

This method is currently banned around the Thames.

John Lamb, the Leigh councillor whose Southend cabinet responsibilities cover fishing, says: "The odd individual or family might rake up a few cockles for their dinner, in the time honoured way, and we would turn a blind eye. But any sign of organised, commercial cockling on the beaches and we would soon pounce on it. We have a good intelligence system out there."

So, although the Maplin Sands rival Morecambe Bay when it comes to dangerous, creeping tides and treacherous sands, there is no prospect - at present - that large groups of cocklers could suffer the same fate as the unfortunate Chinese.

The best concentrations of cockles are found on sand banks stretching across 20 square miles of the Estuary and, especially, on the Maplins.

Since 1969 they have been fished mechanically, not by hand. Specialised boats, using the dredger system, are run by a small group of Leigh families, all with deep roots in the old port.

The most famous are the Osbornes, thanks to their shellfish cafe which greets visitors at the entrance to old Leigh village.

The sand banks are classified as SSSIs (sites of special scientific interest) and must be managed in a sustainable manner.

There have to be enough cockles for birds as well as fishermen.

"Because it is so precious, this has become the most extensively surveyed fishery in the country," says Southend-born Joss Wiggins, chief fishery officer for Kent and Essex Sea Fisheries (KESF).

The fishery authority is anything but toothless. Fishery officers board the cockle boats randomly to check compliance with the regulations. They also conduct an annual audit of the cockle beds.

The fishery authority sets the TAC - Total Allowable Catch - which currently stands at 7,200 tons.

The TAC remains set in stone. "More people might be granted licences, but the TAC would remain the same," says John Lamb. The result, of course, would be smaller portions all round. The conclusion is obvious. "The cockle beds would still be there, but the fishermen wouldn't," says Mr Lamb. "The industry would no longer be viable."

Yet that is exactly the situation that could emerge. Long before Morecambe Bay, the fishery authority was under pressure to grant more licenses.

The history of existing permits is complex, but basically relates to deals that were struck back in the 1960s. These allow a number of fishing families the right to an annually renewable license.

Now other fishermen want a share of what they regard as an unjustified Leigh monopoly.

The threat to Leigh is compounded by the new Gangmasters' Act.

The aim is to curb the sort of ruthless gangmasters who lay behind Morecambe Bay, by imposing a regulated system. Only gangmasters holding a license will be able work in the fisheries.

They too will push hard for the right to exploit Thames Estuary cockles.

For Leigh fishermen this could prove the final straw. "If our quota is cut, there would be nothing to keep us here," says Andrew Laurence, of the Osborne's firm.

Morecambe Bay suddenly seems a lot closer. The events of February 2005 could ultimately prove the end of a tradition that is as iconic to Southend as the pier, not to mention a good deal tastier.