Council officials have found “historic breaches” of planning rules after examining the family cottage Dominic Cummings stayed in during lockdown.
Durham County Council received a string of complaints about the home Boris Johnson’s aide travelled 250 miles to stay in at the end of March.
Now the council has said it found “historic breaches of planning and building control regulations”.
But it did not say what those breaches were, and said no enforcement action would be taken because of a time limit on doing so.
The council has referred separate complaints ” in respect of non-payment of Council Tax” to the Valuation Office for “consideration and review”.
The property on the outskirts of Durham City is where the Downing Street adviser stayed after he and his wife suffered coronavirus symptoms.
According to reports, his parents bought the farm in 1999.
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.
Complaints were made after journalist Alex Tiffin analysed public documents and questioned whether the property had followed planning and Council Tax rules.
Stuart Timmiss, head of development and housing at Durham County Council, said: “We have now investigated the complaints regarding planning permission.
“While there have been historic breaches of planning and building control regulations, current legislation places a time limit on any enforcement measures and as a result no further action will be taken.
“The investigation concluded that the main house has not been sub-divided and that the residential use of an outbuilding for family accommodation does not require planning permission.
“However, advice has been provided in relation to building control.
“We have also looked into the complaints raised in respect of non-payment of Council Tax and will be passing our findings on to the Valuation Office for its consideration and review.”
Downing Street declined to comment today on the council’s statement.
Mr Cummings drove with his wife and young son to the property in late March despite his wife already having possible coronavirus symptoms.
Mr Cummings told a news conference that the building was “an isolated cottage” roughly 50 metres from his parents’ home, and described it as “sort of concrete blocks”.
Hours after he arrived, he too fell ill with coronavirus symptoms as did his son – who ended up being taken to hospital.
He later drove on a further 60-mile round trip to Barnard Castle, testing his eyesight.
The government refused to sack him, claiming his 500-mile round trip to Durham was within the rules despite clear orders to stay at home during the lockdown – especially with symptoms.