Marshlands in Swanscombe have been granted special protected status, dealing a blow to plans for the multi-billion pound London Resort theme park due to be built there.

But conservationists have welcomed protection for a "wildlife haven" close to the M25 and on the Thames, which is home to a rare endangered species of jumping spider.

Swanscombe Peninsula in Kent has been designated a Site of Special Scientific Interest (SSSI) for its grassland, scrub, wetlands, grazing marsh and saltmarsh habitat which is home to an array of wildlife.

The peninsula on the Thames hosts more than 1,700 invertebrates, including the critically endangered distinguished jumping spider, breeding birds such as marsh harriers, reed warblers and bearded tits, and nationally rare plants.

Government conservation agency Natural England also said the 250-hectare (620-acre) site, which lies between the M25 and Gravesend, is important green space for people as well as wildlife.

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The Save Swanscombe Marshes campaign have been calling for the site to be protected, including a SSSI, with Buglife, the RSPB and Kent Wildlife Trust groups all making a united call to save the "wildlife haven."

The news deals a big potential blow to plans for a new theme park, the London Resort, on much of the peninsula, which the company behind the scheme says will bring jobs, money and regeneration of a brownfield site, while still providing areas of environmental enhancement and wildlife habitat creation.

Dubbed the UK's answer to Disneyland, the theme park contains to twin parks across a 535 acre site, the first potentially opening in 2024.

But wildlife groups say the nationally important wildlife area, which receives protection with the SSSI designation, should not be developed.

News Shopper: The London Resort is due to be built on Swanscombe Marshes - Spider (c) Roman Willi. Marshes (c) Daniel GreenwoodThe London Resort is due to be built on Swanscombe Marshes - Spider (c) Roman Willi. Marshes (c) Daniel Greenwood

They warn the proposed development has been designated as a Nationally Significant Infrastructure Project and will not go through the normal planning process but will be decided by the Government.

Natural England said the designation of the site for its nationally important wildlife features is an important step towards ensuring its environmental value is recognised and taken account of in any future planning decisions.

James Seymour, Sussex and Kent area manager for Natural England, said: "The designation of Swanscombe Peninsula as an SSSI is great news for one of the richest known sites in England for invertebrates, ensuring essential refuge for many rare and threatened species that sadly are not able to thrive in the wider landscape.

"This area is living proof that some of our most important species can thrive hand in hand with businesses and transport infrastructure. Special places like this will form the vital backbone of a national nature recovery network."

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Matt Shardlow, chief executive of Buglife, said: "We thank Natural England for doing the right thing by protecting one of the country's most important wildlife sites.

"However, the Swanscombe Peninsula remains under threat and it is crucial that a precedent isn't set by allowing a fun fair to be considered as more important than the wildlife that inspires wonder and sustains us."

Richard Bloor, from Kent Wildlife Trust, said: "We must ensure that the Swanscombe Peninsula, alongside other SSSIs, are fully protected from any further development, and brought into better condition as part of the Nature Recovery Network, ensuring that the UK becomes a less nature-depleted place whilst tackling the nature and climate crises."

Emma Marsh, RSPB England director, said: "Recognition as an SSSI should end any debate about developing a theme park here.

"The focus should immediately turn to how Swanscombe Marshes can be effectively managed and monitored so that the species and habitats continue to thrive with their newfound status."

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But PY Gerbeau, chief executive of London Resort Company Holdings, said: "The project will of course continue, and this is just another issue to address in the long history of this project."

He said the company had been surveying and monitoring the site since 2012 and was working closely with Natural England to identify the right ecological solutions to deliver the project.

He added: "Sustainability is a green thread throughout the London Resort proposals and we're very proud of that.

"We have demonstrated, across thousands of pages within our application, our vision to deliver a net gain in biodiversity and our commitment to enhancing and managing habitats.

"(It is) an investment that runs into millions because we believe in sustainability and in our role as custodians of the environment."