People living near Manthorpe Lodge, in Lodge Way, alerted the council's planning department after seeing activity on the derelict site.


Residents have opposed plans to demolish the Victorian mansion and replace it with 24 flats and permission was refused by SKDC in October.


SKDC said developers' representatives were on-site for "routine matters" and that a planning officer had also visited the site.


A spokesman said: "An officer did speak to the developer and advised that he would need to submit an application for what is known as Prior Approval to demolish and that if he did demolish before this had been granted, he could be subject to enforcement action."


District councillor Ray Wootten, who represents the area, said residents will continue to oppose demolition of the building.


He said: "A fine building has been left to deteriorate on such a prominent corner in the town.


"The residents want the site re-devloping but are opposed to the plans for flats. They want something in keeping with the area and certainly do not want the building demolished."


Manthorpe Lodge was once the home of industrialist Rothwell Lee but has been abandoned for several years.


In December 2005, arsonists set fire to the annexe of the building, which has been regularly targeted by vandals and thieves who have taken fittings, including fireplaces.

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