Kent's coastline is under serious threat of flooding - with whole stretches set to disappear in decades.

That is the grim warning of the new head of the Environment Agency.

Lord Smith of Finsbury, who was appointed the agency's chairman last month, said Britain faces hard choices over which areas of our coast to defend and which to allow the sea to reclaim.

The life peer and former Secretary of State for Culture pledged to investigate engineering possibilities in a bid "to defend communities where there are significant numbers of properties under threat."

He said: "This is the most difficult issue we are going to face as an agency. We know the sea is eating away at the coast in quite a number of places, primarily, but not totally exclusively, on the east and south coasts."

He said: "We will publish next year details of the work that's been done, where we think the particular threats are, where we think there is current defence in place. We will begin to talk with communities where we think defence is not a viable option."

In a wide-ranging interview Lord Smith also warned the government of the potential environmental impact of a series of key projects, including the buildiing of a third runway at Heathrow. He said the plans to build a new coal-fired electric power station at Kingsnorth should be scrapped until the government is certain it will not pump out harmful gases.

International environmental action group, the World Development Movement (WDM), said this week current models for climate change predict that without serious action to cut emissions the sea level in Kent could rise by 74cm by 2080, leading to many parts of Kent being flooded.

Murray Benham, head of campaigns at WDM welcomed Lord Smith's comments. He said: "The government must take heed of this warning. It is absolute folly to push ahead with climate - damaging projects like the new coal power station at Kingsnorth. Climate change is not only threatening huge swathes of the UK’s coastline but also much of the land where the poorest people in the world live. We hope that Lord Smith will continue to use his influence to put real pressure on the government to drop these proposals."

Factfile:

A wide range of different coastal defence structures can already be seen around the Kent coastline , including

Groynes - structures of rock and timber situated in the sea to control beach movement such as those at Whitstable and Dymchurch

Breakwater - rock or concrete arms to protect an area from wave action can be seen at Herne Bay

Revetment - a sloping stone or concrete surface to protect shoreline from wave action such as the ones at Reculver or Folkestone Warren

Beach replenishment - the mechanical import of material to a beach such as done at Hythe

Beach reprofile - the movement of beach material from downtide to uptide