Felixstowe port is one of four sites being considered for development

Under the slogan Portswatch, the charities are about to publish a manifesto calling for better government controls on how new ports are built.

Ports are planned at Dibden Bay in Southampton, London Gateway in Essex, Felixstowe and Bathside Bay in Harwich.

Portswatch says valuable wildlife sites will be lost if the ports go ahead.

The coalition is made up of the Royal Society for the Protection of Birds, The Wildlife Trusts, Friends of the Earth, Transport 2000, the Whale and Dolphin Conservation Society, The Wildfowl and Wetlands Trust, the Marine Conservation Society and the Campaign to Protect Rural England (East of England).

Portswatch says it accepts ports are essential for the economy and that more capacity is needed for container ports.

But it says if all four ports are built they will provide almost twice the capacity the industry says it needs - leading to needless loss of habitat.

Long-term impact

Paul Davey, of Hutchison Ports Holdings, which runs the Port of Felixstowe and hopes to build at Bathside Bay, said: "The port industry's due to run out of container capacity by some time around 2008 at current rates of growth.

Portswatch says coastal habitat is in danger

"It's crucial that we provide more capacity to safeguard the future of the UK economy."

The company is offering to replace the salt marshes and mudflats it would destroy by building a new port at Bathside.

But scientists are unsure of the long-term impact of the port on the environment.

Dr Alastair Grant, of the University of East Anglia, said: "I would guess that something reasonable will develop [at Bathside] but that is very much a guess and until we let the sea in no one can really predict with certainty what's going to happen."

Government strategy urged

Portswatch wants all four port proposals put on hold until it is shown best use is made of existing ports.

It is also calling for a method of determining the possible need for greater port capacity to be agreed.

The government hasn't done the necessary work to decide which of the four major proposals that are currently in the planning system is the right one Duncan Hugget, RSPB

Duncan Hugget, of the RSPB, told the BBC: "The government hasn't done the necessary work to decide which of the four major proposals that are currently in the planning system is the right one."

Portswatch claims government strategy and guidance on the super-ports is almost non-existent.

It has called for a national strategy showing a preference for the best port developments based on environmental impact, transport and social factors.

That call was backed by a Commons transport select committee report last November.

It recommended government forecasts on port capacity to ensure planning at national level, and a more active government role in developing environmental standards for ports.

A Department For Transport spokesman said: "We are aware of Portswatch's concerns and the Department for Transport will be formally responding at the end of this month to similar comments made by the House of Commons transport select committee in their November 2003 report on ports.

"The cases concerned are currently within the planning approvals process and it would therefore be inappropriate for ministers to comment."