A council is investigating complaints that the property Dominic Cummings used during his lockdown trip did not have the correct planning permission.
The PM's adviser stayed with his family in what he said was a "cottage" on his parents' farm in Durham, in April.
The only planning applications listed on the council's website for the farm are for a roof over a swimming pool in 2001, and the removal of various trees.
Durham County Council and a local MP have received a number of complaints.
Downing Street has declined to comment.
The Cummings' family property, North Lodge, is on the outskirts of Durham.
The City of Durham Labour MP Mary Foy, whose constituency includes the home, said she had also raised questions with Durham County Council.
She said she had received a number of complaints from constituents, and had asked the council whether the property Mr Cummings stayed in had proper planning permission, and whether it was registered for council tax.
She has yet to receive a reply.
The council investigation was first reported by The Northern Echo.
Mr Cummings' trip to Durham with his wife and child caused a political fallout with The Scottish National Party's Westminster leader Ian Blackford saying Mr Cummings should resign or be dismissed by Boris Johnson for making the journey. Mr Cummings said he acted reasonably and legally.
Prime Minister Boris Johnson's positive test for coronavirus was announced on 27 March, and Downing Street said at the time Mr Cummings did not have symptoms.
Later that day the adviser drove to the north-east of England.
On 30 March, it was confirmed Mr Cummings had developed symptoms of the virus and was self-isolating at home.
Durham Police later said he might have broken lockdown rules with a subsequent trip to nearby Barnard Castle, but added that if he had broken the rules it would have been a "minor breach".