A battle is brewing after one of the world's biggest theme park operators said plans for a rival £2.5bn project in Kent should be withdrawn on legal grounds.

Leisure giants Merlin Entertainment – which runs some of the biggest attractions in the UK including Legoland, Sealife and Thorpe Park – say they are taking legal advice over the resubmission of plans for the London Resort.

It comes after bosses at London Resort Company Holdings (LRCH), the company behind the park proposed to be built at Swanscombe between Gravesend and Dartford, were granted an extension to redraw plans after the site was granted special habitat protection in March.

As a result, planning inspectors reviewing the theme park bid allowed an additional four months for amended plans to be produced and submitted ahead of a full examination due later this year following a request by LRCH.

Merlin's chief corporate officer Matt Jowett has now written to the Planning Inspectorate claiming LRCH is using the opportunity to change aspects of its application unrelated to the awarding of SSSI (Site of Special Scientific Interest) status for the Swanscombe Marshes.

He said the plans should be withdrawn and the entire application resubmitted due to the fundamental changes taking place from the application inspectors first considered as acceptable for inspection in January, allowing the next stage of the planning process to take place.

Mr Jowett said Merlin, whose portfolio also includes Madame Tussauds and Alton Towers and is second only to Disney in visitor numbers globally, had taken legal advice which said details of the plans submitted after the SSSI extension "were not consulted upon at the statutory consultation stage so that proper consultation was not carried out prior to submission of the application".

He added: "They [LRCH] include a document described as 'Supporting Resort and Leisure Market Assessment', which plainly has no direct relevance to the SSSI status.

"There are multiple changes to application plans and other application documents. The submissions by LRCH make no reference to consultation with the public and no reference to consultation with interested parties such as ourselves."

LRCH submitted its planning application to the Planning Inspectorate in December with officers accepting it was complete enough to be assessed.

The bid is currently at the pre-examination stage allowing detailed comments to be made by interested parties, such as councils, nearby businesses, transport operators and residents.

But Mr Jowett said information now being submitted was not part of the original application and means it "may well have resulted in different responses from the public or other stakeholders".

He said this risked the planning process "has not been properly carried out" and could be subject to a legal challenge.

In order for people to have "sufficient time" to assess and comment on new plans, Mr Jowett said the plans should be "withdrawn and resubmitted" or could lead to the process "jeopardising the examination process and any decision that follows".

He also called for a consultation on "material changes" to the application such as the market assessment and business case details which is due to be submitted by LRCH as a new document in response to the SSSI award.

Speaking last month, resort boss Pierre-Yves Gerbeau said there were no plans for any "material change" to the application but admitted there would have to be amendments after Natural England awarded status to the Swanscombe Marshes to protect the greenland and endangered species which live there.

Wildlife charities which fought for the protection of the site also wrote to inspectors last month saying the plans should be withdrawn.

They said 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".

In earlier submissions, Merlin said the case had not been demonstrated for a new theme park proposed by LRCH adding claims they had not "accurately portrayed" the existing visitor attraction market.

"The Examining Authority (the Planning Inspectorate) should identify 'need' as a 'principal issue' to be fully assessed during the examination stage – whether the applicant is able to demonstrate a need for the development. It is our position that this aspect is self-evidently both important and relevant to the Secretary of State's decision."

The company added it felt LRCH had presented "a number of unsubstantiated and potentially inaccurate assumptions" which had led to benefits of the scheme being "significantly overstated" because it had not offered "a sound, factual, evidential or policy basis" to be granted permission.

Mr Jowett's comments have been echoed by the chief executive of the British Association of Leisure Parks, Piers and Attractions, Paul Kelly, who said: "Arguably, this document should have been submitted with the application at the end of December 2020, as it is likely to be highly relevant to the issues under consideration in the determination of the London Resort proposals.

"Particularly now that you have identified “the nature of the UK’s existing visitor attraction market and the effects on existing theme parks and resorts, including diversion” as a principal issue to be examined.

"Given the discretion you are exercising in allowing such additional documents to be submitted, I would respectfully ask that you further exercise your discretion in re-opening the period for relevant representations being made, in order to allow potential interested parties to respond."

Papers filed by LRCH show it is planning to redraft some 203 documents submitted as part of the plans so far, producing two new documents and continuing to update five "live documents" as the examination progresses.

A spokesman for the Planning Inspectorate did not confirm if the matters raised by Merlin had been considered yet and inspectors were still judging the "principal issues" of the application following the documents submitted and representations received so far.

After this a formal "preliminary meeting" would take place to "agree the timetable for the examination and what matters need to be considered" and the six-month examination phase would start the following day.

"As a result, we are not in a position to comment on the application at this stage," the spokesman said.

A date for the preliminary meeting has not been set.

LRCH did not respond to a request for comment.

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