Council planners have said they are considering "a number of complaints" received about the planning permission status of the cottage where Dominic Cummings stayed on his parents' farm.
Durham County Council said it was looking into the matter regarding the outbuilding on the farm on the outskirts of Durham city, where the No 10 adviser stayed with his wife and son after experiencing coronavirus symptoms.
Mr Cummings told a news conference last week that the building was "an isolated cottage" roughly 50 metres from his parents' home, and described it as "sort of concrete blocks".
According to reports, his parents bought the farm in 1999 and records on the county council planning portal show that permission was granted two years later for the erection of a pitched roof structure over an existing swimming pool.
In subsequent years, permission has also been granted to fell trees.
A council spokesman said: "We have received a number of complaints and are currently looking into the matter."
Durham City Labour MP Mary Foy has also written to the council to ask about any potential planning permission issue, after she was contacted by constituents.
She said: "We had quite a number of emails about it."
Downing Street declined to comment when asked about the issue during a Westminster briefing.