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Campaigners in north Devon will go to the High Court on Monday to try to prevent a caravan park in Croyde expanding.
Ruda Holiday Park has been granted the legal right to develop a previously unused field, but local residents say the decision was based on a mistake in the original planning application.
The park says its relationship with residents is very important, adding it has followed all necessary planning processes.
The case is now going all the way to the High Court in London.
The residents association says it understands the importance of tourism in Croyde, which depends on the money it brings into north Devon every year. But they also say one of the main things that attracts people to the area is its outstanding natural beauty, which they fear could be put at risk.
The Croyde Area Residents Association (CARA) claims the park has only been granted a Certificate of Lawful Development because mistakes were made seven years ago during an application to North Devon District Council to extend the park's opening dates.
Jane Young, from CARA said: "Everybody just thought they were dealing with the opening hours and they didn't realise they had granted massive expansion of the holiday park.
"It's a very important case for our village, it's a very important case for the area of outstanding natural beauty."
Campaigners fear the development could be used as a precedent to allow further expansion in future.
CARA chairman Steve Vine said: "There's no more checks and balances as to the environment or as to water runoff, various traffic issues, all those sort of things. They can just actually expand in their own interest and that's what we think in Croyde and CARA, that's what we think is wrong."
They're going to the High Court for a judicial review to challenge the original 2014 planning application.
North Devon Council says it will not comment until the legal proceedings have concluded.
The owners of the park say their relationship with local residents is very important.
In a statement, the company said: "We have followed all necessary planning processes and procedures and are in frequent dialogue with the local parish council and planning authorities. Given the legal process is ongoing, it's not appropriate to comment further".
The case will be heard at the High Court on Monday.