From the outside the property still looks like an ordinary farm building, made of unpainted grey concrete blocks with a big sliding door and no windows.

But inside it has four bedrooms, a kitchen, living room and bathroom facilities and flourescent lighting and radiators.

Planners say the occupants ‘deliberately concealed’ the property and the only clues to its use are a letterbox on an entrance gate and a satellite dish on a wall away from the road.

The owners had previously lived in the adjacent farm which they sold in 2008 and then bought the pigsty and other agricultural buildings.

The 3,293sq/ft shed, named Heathacre Barns, stands in the middle of the Norfolk Broads surrounded by farmland and waterways.

The local Broads Authority said the owners failed to get any planning permission to convert it into a house.

They began investigating it in November 2012 after being refused access to the site to check out a rat infestation.

Four months later the council ordered the owners to get out and return it to its former use.

The unnamed pair appealed to the planning inspector but lost and have been told to move out by this weekend.

As a result they have put the pigsty up for auction with a guide price of just £20,000 – and a warning that it cannot be used for residential purposes.

They will have to strip out all the furniture and fittings and return the barn to its original state.

A report by a council planning officer said: “It should be noted that it is considered that there has also been a deliberate attempt at concealment of this development.”

A Broads Authority spokesman said: “The couple converted the barn without planning permission.

“We asked them to remove everything and move out and they appealed against it so the case went to an independent planning inspector who supported us.

“They have to be out by Saturday and we will be inspecting the building to make sure they have removed the kitchen, bathroom and everything else they put inside.

“It can only be used as an agricultural building, which is why it is only #20,000.”

The couple own a second barn on the site in Chedgrave and previously owned a nearby house which they split into two properties and sold on.

Until they find a more permanent home they will be renting a room from the neighbours they sold their property to.

An enforcement order published by the Broads Authority in 2013 says the local planning authority started investigating the “former piggery” in November 2012.

It says the building has a “shallow pitched roof and no windows” and that the conversion is “not of high quality”.

The enforcement also referenced a pile of cages outside the building which had been used to house chinchillas.

It claimed the owner had advertised the pets on the internet but that they were “not an agricultural animal” was a “development which requires planning permission”.

Robert Hurst, from Auction House, said the property will go under the hammer with a guide price of £20,000 to £40,000.

It is being sold at Dunston Hall Hotel in Norwich on February 18 at 11am.