Developers behind plans for a multi-billion pound theme park are set to make a host of changes to their plans after the proposed location was designated a wildlife haven.

The London Resort proposes to build a £2.5bn entertainment resort on the Swanscombe Peninsula between Dartford and Gravesend.

Earlier this month the project was granted a four-month delay to revise proposals after the marshlands were designated a site of special scientific interest (SSSI) by Natural England.

But developers say they remain "upbeat" and are not planning any "material change" to the bid.

However, in a document submitted to the Planning Inspectorate bosses set out a raft of "substantive changes" to be made in light of the SSSI notification and transport concerns, while other areas are earmarked to receive minor updates, additional survey work or no changes at all.

In the meantime four wildlife charities have penned a letter to the government's planning arm urging theme park bosses to pull out of the project.

They say developers should have "sought to withdraw their existing application" and start again, adding "it is reasonable to expect that proposed changes will result in a materially different project".

Speaking after the site's designation as a "wildlife haven", RSPB's England director Emma Marsh 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."

Jamie Robins, project manager at Bugslife which supported the application for SSSI designation, said plans to erect a theme park on the marshlands were "completely incompatible" with sustainability aims.

"The value of the site for wildlife has been undervalued the whole way through," he said. "There is no sustainable way of building on a nationally important wildlife site."

Environmental campaigners also pointed towards what they perceived to be "inaccuracies" in the original selection of the site and the assessment of alternatives.

But theme park bosses remain steadfast in their convictions of creating an entertainment resort on the Peninsula and say they are not considering other sites.

“The mood is incredibly upbeat," said London Resort chief executive Pierre-Yves Gerbeau.

"The prospect of approval went up enormously after acceptance and we are on track to create a beacon of world class entertainment and experiences within a world leading sustainable environment."

More than 20 years ago the French entrepreneur was parachuted in to save the oft-criticised Millenium Dome Project, now the 02 Area in London.

He says the challenges presented by the Swanscombe Peninsula, also set on a former brownfield site, are "not unusual" and he expects construction to begin next year.

"Our vision of creating thousands of jobs, generating substantial economic growth and a huge boost to tourism within the UK remains as exciting and as deliverable as ever," he added.

Following the SSSI designation Mr Gerbeau said it was "right and proper" to delay and review concerns, adding it was "fundamental" as part of their goal to be "leaders in sustainability".

“The mood is incredibly upbeat"

"We’ve already committed to spending around £150m on remediation, habitat enhancement and providing around eight miles of footpaths and public rights of way," he said.

“But it is right and proper that we take a short extension to revise our reports and ensure they address the issues raised.”

Last month developers revealed plans for Base Camp, a new "pre-historic" zone at the park, featuring one of the fastest rollercoasters in Europe.

Alongside the fun and adrenaline, the land is also set to deliver educational opportunities with an enormous play area for youngsters to explore, excavate exciting fossil finds and develop STEM skills.

The Planning Inspectorate has set out strict obligations and deadlines for Resort bosses as a condition for its decision to grant an extension.

This includes monthly progress reports, a comprehensive list of the documents that will be submitted and a programme setting out when they will be submitted.

KMTV reports as the latest London Resort plans are unveiled

If approved, the theme park will be the first European development of its kind to be built from scratch since the opening of Disneyland Paris in 1992.

It will feature two theme park gates, a water park, conference and convention centre and e-Sports facilities.

Image rights deals have already been struck with the likes of the BBC, ITV and its original namesake, Paramount Pictures.

But the BBC's studio arm was urged to withdraw from the project amid claims of incompatibility with its aims of "creating a positive environmental impact".

A six-month formal examination period will commence later this year.

After this it will be the government which will have the final say over whether the plans, earmarked as a nationally significant infrastructure project, will get the green light.

Read more: All the latest news from Dartford