The twist emerged this week after Fairfax Media revealed that the inner south dual occupancy was treated differently from the other dual occupancy blocks contaminated with Mr Fluffy asbestos, and was also treated differently from other Fluffy homeowners in the scheme to demolish more than 1000 homes.

There is no suggestion Mr Barr's brother, as a tenant, not an owner, had anything to gain from the special deal.

Fluffy owners on dual occupancy blocks and other unit-titled properties are not being given the first right to buy back their land once the house is demolished, unlike the other Fluffy owners. The government says this is because dual occupancies are more complicated and take longer, involving negotiations and permission from the neighbours behind.

But the owners of the inner south property were given a deal to buy back their land as part of the buyback - in an arrangement that needed ministerial approval and that was described by asbestos taskforce head Andrew Kefford as "genuinely unique".

The arrangement required ministerial approval and was signed off by then deputy chief minister Simon Corbell. It has now emerged that while Mr Barr was the minister responsible for the Fluffy buyback at the time, Mr Corbell was given the task of considering the inner south deal because of the involvement of Mr Barr's brother. The government decided that would resolve any perceptions of conflict of interest.

The owners were also treated differently from other Fluffy owners in being given the price for re-purchasing their land upfront. Other Fluffy owners must wait until their houses are demolished and the land is ready for sale before it is revalued and offered back to them - leaving a gap of up to three years, possibly more, between the time their house and land was valued for purchase by the government in October 2014 and the time their land is valued for buying back.

The asbestos taskforce said it had to make a special deal with the owners because the property was part of a duplex (separate to the backyard dual occupancy property rented by Mr Barr's only brother). The owners of the other side of the duplex wanted to do a private demolition, meaning there was pressure for a resolution - to get one side demolished, they had to get agreement from the other side.

Mr Barr's brother moved to the inner south property with his family in mid 2014, renting the house behind the Fluffy duplex. He and his family stayed there until about August 2016 when they bought a new home and moved.

The deal with the duplex owners was signed in mid 2015, with settlement later that year. The demolition was to happen almost immediately but experienced a series of delays, and did not happen until the end of July 2016.

Mr Barr's spokesman said the chief minister was never briefed on the deal and he did not speak with Mr Corbell about it. Mr Barr had instructed the taskforce to engage with Mr Corbell on the matter to remove any doubt about perceived conflict of interest, he said. Demolition had been delayed because it was a complex case, he said.

"It is not surprising that a politician's relative would be one of the tens of thousands of Canberrans who have lived next door to a Mr Fluffy house," the spokesman said, suggesting that Mr Barr's family was being used to "smear" him.

"They rented this neighbouring house for a short time. They had no benefit from any part of this process."

Asbestos taskforce head Mr Kefford said the property was not surrendered until November 18 2015 and it was demolished "following the resolution of the range of complexities associated with this particular set of circumstances".

"This included the completion of a development application process, resolution of contractual and personal arrangements with the owners of the two halves of the affected duplex, works required to shared utilities and the appropriate community engagement," he said.

Asked what contact the taskforce had had with Mr Barr's brother, he said, "The only contact was as part of routine engagement with the occupants of neighbouring properties in relation to the development application process, demolition process and timing, access and work to utilities."