Pressure is mounting on the government to confirm protected status awarded to marshland where a huge theme park is proposed to be built.

The Swanscombe Marshes, between Gravesend and Dartford, could host a £2.5bn attraction dubbed the UK's answer to Disneyland if it is given the green light.

But environment groups fighting to protect the land – home to rare species and is an important habitat for vast numbers of animals and plants – have urged the government to ratify the Site of Special Scientific Interest (SSSI) status granted by Natural England in March.

Buglife, RSPB, Kent Wildlife Trust and CPRE Kent joined forces to campaign for the greater protection for the site.

A consultation into the SSSI status award closed yesterday and the four groups say it is vital for the government to confirm it so the area has full legal protected status.

Craig Macadam, director of conservation at Buglife said: “Recent surveys have revealed that the Swanscombe Peninsula is one of the most important sites in England for rare invertebrates.

"However the site could be lost if plans to build the new London Resort theme park are approved, so we really need the notification swiftly confirmed and the site afforded full legal protection.”

The RSPB has repeated its calls for the theme park plans to be withdrawn and said it was "inappropriate" to be regarded as a nationally significant infrastructure project – something normally reserved for major roads, airports or power stations.

Nick Bruce-White, RSPB operations director for southern England, said: "This theme park must not take precedence over the species and habitats that it threatens; the developers must withdraw their application.

“If the SSSI is confirmed, and the development is still consented, it will be one of the largest ever single losses of nationally protected habitat in UK. We cannot allow this to happen.”

It comes as planning inspectors told bosses behind the theme park bid to clarify several points in their application.

The Planning Inspectorate (PI) team examining the London Resort plans have asked for further detail on the project's "reasonable worst case scenario" of the size, height and placement of each building and structure.

Maximum and minimum dimensions have been requested in updates to submitted documents after an initial assessment by the PI found the park would not fill the full parameters of the site.

The panel has also asked for details on how much of the site the buildings and structures could occupy if they are not filling the entire allocated space.

It has suggested providing a list of the range of the size of buildings in 10m bands such as from 0-10m, 10-20m, 20-30m.

The letter from the PI, published on the examination website, comes after London Resort bosses sought "flexibility" in how the plans would be assessed.

Documents submitted as part of the application for a Development Consent Order by London Resort stated they would need "flexibility for the detailed design of certain elements" of the plans.

The panel has now set out its requirements for London Resort to provide "sufficient information" about the proposals to ensure the examination runs efficiently and assesses the "worst case scenario" of the development and its environmental impact.

Government guidance states this is acceptable when it is "not possible to define a project fully in the short term" and requires the examination panel to set "clearly defined and reasonable parameters".

It does not "remove the onus on applicants to submit as detailed as possible project proposals in their application, and it should certainly not be an excuse for an unnecessary degree of flexibility".

Advice shared in a letter by lead PI panel member Stuart Cowperthwaite published this week added his team and the Secretary of State "will need to be satisfied that, given the nature of the project, they have full knowledge of the likely significant effects on the environment".

Meanwhile campaigners say the plans, if approved, would contradict the government's pledge to protect 30% of land for wildlife by 2030 and argue it would set a dangerous precedent for future projects and put habitats at risk.

Julia Hunt, head of advocacy at Kent Wildlife Trust, said: “Government is clear on its ambitions for nature. But it needs to turn words into action and step up to prevent our best sites being lost to development.

"If it does not protect places like the Swanscombe Peninsula it will be failing in its ambitions to make the UK a nature rich nation and failing people who need nature.

"Wildlife needs these places, and people, particularly in urban areas, need these places.”

The marshes are home to more than 200 species.

London Resort bosses have also been asked to justify the "extent of flexibility" required, provide evidence to support it as well as it being clearly defined to allow assessment of the environmental impact and ways to deal with it.

New images and visuals showing the more precise measurements of the buildings and structures have also been requested.

Mr Cowperthwaite said this should show "reasonable worst-case scenario scaling, massing and rendering of the proposed development for both daytime and night-time".

He added it would be useful for the panel to see recommendations of existing developments comparable to the London Resort proposals and will have similar "visual and landscape effect".

The applicants, London Resort Company Holdings, have been given until July 21 to submit a response as to how it will be responding ahead of a site visit in September.

Tourism giants Merlin Entertainments, which run Alton Towers, Madame Tussauds and Legoland, have also raised concerns about the application saying it needed to be withdrawn.

The company said changes being made to incorporate the SSSI status following a four-month extension also included changes outside its scope which amounted to "material changes" of the application which needed to be fully consulted and reconsidered.

But Mr Cowperthwaite said last month the examination of plans could continue and any material changes would be assessed "as and when" new documents were submitted.

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