Wintering birds travel to the marshes from further north

Elmley Marshes, on the Isle of Sheppey in Kent, is already a National Nature Reserve and is one of the most important wetland habitat areas in the country.

During the winter, the marshes are home to around 200,000 birds.

The designation coincides with work by the Royal Society for the Protection of Birds (RSPB) on a new hide at the reserve and the creation of new islands.

Workers have dug out 15 years of accumulated mud to create the islands, which have already attracted wintering birds.

The reserve will expand by 330 acres - equal to 300 football pitches

High-tide roost figures for the area this autumn already include 2,600 dunlins, 300 grey plovers and 30 bar-tailed godwits.

Alan Johnson, of the RSPB, said: "Elmley Marshes is internationally important for wildlife.

"There are tens of thousands of widgeon, thousands of teal, thousands of golden plover, grey plover, dunlin, redshank and lapwing.

"All these birds are coming from countries further north where they breed, because we've got a massive abundance of invertebrate food for them here."

The RSPB was one of the organisations that recently fought plans for an airport on the north Kent marshes at Cliffe, on the Thames Estuary, which is also home to hundreds of thousands of birds.

The proposal for an airport at Cliffe was thrown out by the government Aviation White Paper, published this week.