Enforcement notices have been served on the Occupy camp outside St Paul's Cathedral in the latest attempt to remove hundreds of tents that have been pitched in the heart of London's financial district since mid-October.

The notices, which were served during Wednesday's strike, took camp members by surprise, as many were out protesting cuts to public sector pensions. The notice forms part of the Corporation of London's legal proceedings against the tented village after St Paul's pulled out of similar action a month ago.

The corporation, one of the smallest local authorities in the country, says it has spent £450,000 on policing the camp, £15,000 on cleaning and has budgeted £200,000 for legal fees that will come out of the corporation's public purse.

The enforcement notice warned activists that the camp was not "an appropriate use of land".

"It adversely affects the setting of the cathedral and other listed buildings and does not preserve or enhance the character and appearance of the St Paul's conservation area. It adversely impacts other uses in the locality including worshippers and businesses," it said.

However, during the corporation's regular common council meeting, Stuart Fraser, chairman of the policy and resources committee, admitted that environmental health officers found no health and safety threat to workers or tourists around St Paul's. He also reported that the court case that is due to begin in the high court in a few weeks could last until mid-January when time to appeal was taken into account.

Protesters will have 48 hours to comply with the notice, which takes effect on 30 December unless an appeal is made beforehand.

In response to a question from ward, Brian Mooney as to why the Corporation hadn't responded to three "anodyne demands" about opening up the City's accounts, Fraser said that members should not capitualate to demands from an "ad hoc" group.

Fraser added that details of Corporation's secret cash account could be revealed if councillors so wished but they should not be intimidated by it.

The activists, who are campaigning for economic and social justice, have three bases, one of which is on corporation land. Of the others, Finsbury Square is on land owned by Islington council, and the third is non-residential and operates from a vacant bank building near Liverpool Street.

The Corporation also said that they had identified 15 vulnerable people who were attending the camp because of the free food, tea and company which it provided and that policing the camp and put a "considerable" strain on City of London police.

Protesters will have 48 hours to comply with the notice, which takes effect on 30 December unless an appeal is made beforehand. The eviction hearing will take place at the high court on 19 December.

• This article was amended on 2 December 2011. The original misattributed a description of the camp as a "cancer" and a "disease" to Stuart Fraser. He did not use that term. This description was used by another councillor at the meeting.