Police today called for co-operation from protesters against a new housing development.
Campaigners against the 850-home scheme in West Durrington, near Worthing, are organising a vigil at the proposed site in Titnore Lane next Saturday.
But police have not been officially notified and fear the protest could become unruly.
The long-running planning dispute has led to clashes between protesters, councillors and developers in the past.
Tensions ran high when planning permission for the development was granted in June by Worthing Borough Council.
Police ejected noisy protesters from the meeting after they stormed the stage, blowing hooters and waving banners.
In August demonstrators from campaign group Protect Our Woodland set fire to an effigy of John Prescott, holding up dozens of motorists to show their defiance at plans to axe some 210 trees.
Previous demonstrations have attracted hundreds of campaigners and led to minor scuffles and arrests.
Next Saturday's site occupation has been called by the newly-formed Titnore Emergency Action (TEA) for 2pm.
Superintendent Lance Gray, said: "Section 12 of the Public Order Act 1986 places a requirement on the organisers of assemblies and processions to notify the police in writing of the date and time and details of the organisers. This has not taken place."
Notice of the demonstration has spread by word of mouth and community websites in Worthing.
Supt Gray added: "Anyone who is organising this protest is urged to contact me."
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