The contents of a historic country mansion where band Girls Aloud went ghost hunting are to be auctioned off.

Plas Teg near Mold, Flintshire, has a more than 400-year history – it was constructed in 1610 as was said to be one of the most advanced houses in Wales at the time.

It has played host to Jacobean courtiers, served as a country residence, and even been used as army barracks and auctioneer’s warehouse, as well as being one of the settings for UK girl band Girls Aloud’s ghost hunting endeavours.

But the owner, now in her 80s, has decided it’s time to let someone else enjoy its contents, worth hundreds of thousands of pounds.

Plas Teg was rescued from near-collapse in 1986 by antique dealer and interior designer Cornelia Bayley, who has announced she will be putting its entire contents up for sale with auctioneers Rogers Jones and Co.

Dr Mark Baker – an author, trustee of the property and family friend of Ms Bayley – recalled visiting the mansion during his childhood.

“Cornelia had such a vision for the house, she wanted it to be something which the original inhabitants might have been living in today, rather than a time capsule of the 17th or 18th centuries,” he said.

“So it was always furnished with highly decorative pieces to her taste, from all periods, and from all over the world.”

The property has featured in several TV shows, including Channel 4’s Country House Rescue and Ghost Hunting with… Girls Aloud on ITV2.

Ben Rogers Jones, one of the auctioneers, said it has one of the hardest collections he has ever had to value.

“The contents bear little if any relevance to the period of the house. They range from ancient Chinese to 1950s reproductions, and represent very little other than Cornelia’s own highly developed and eclectic taste,” he said.

“I am hopeful that the entire collection will raise in the hundreds of thousands, though there are items ranging from £50 to well into five figures.”

Plas Teg was conceived in the early 17th century by James I’s courtier, Sir John Trevor, as a “prodigy house”, on part of a processional route for the then Prince of Wales.

Henry Frederick, Prince of Wales, was travelling to Ireland, to be confirmed as King in the event of the death of James I.

But he died before he could ever accede to the throne, and future Charles I became heir. Had he not died, some historians believe there would never have been an English Civil War.

After Henry Frederick’s death, most of the dozens of plans for processional homes across Britain were shelved, but because Plas Teg had already been in an advanced state of construction, it was allowed to be finished.

“It differed from most of the baronial homes in Wales, as it wasn’t a squat hall, it had several stories,” said Dr Baker.

“It was built on the latest designs from Italy and Spain, and used architects who were working on royal properties in Kent.

“Rather than everyone living together around a fire, it was divided up into public and living quarters as you’d see in a modern house; so you can see the levels of effort and expense which were taken.”

Yet the civil war did happen, and Plas Teg became one of thousands of properties to fall foul of it.

But, though it was raided, “it was spared the worst of destruction which happened to many other homes in Wales”.

The 10-bed mansion was passed down through generations of the Trevor family until World War Two, when it was requisitioned by the government.

In 1945, it was sold to Dodds the Auctioneers as a warehouse, who applied to have it demolished.

Patrick Trevor, an ancestor of the original family, tried to save it but, after it changed hands several more times, Cornelia Bayley eventually purchased it in 1986.

She spent £200,000 of her own money on renovations, before opening it to the public.

“When she took it over there were trees growing through the roof and pigeons flying around inside,” said Dr Baker.

“There’s no doubt that Cornelia has saved Plas Teg for the nation, but now it’s time to pass on the baton to the National Trust or the Landmark Trust, while the sale of her contents should hopefully fund her care in her older age.”

Although Cornelia is physically well, the strain of up-keeping such a large property has become an increasing strain on her, in her 80s.

Cornelia has largely withdrawn from public life, nevertheless she is incredibly keen to see the work she has started continued by somebody equally enthusiastic.

The online auctions began this week and will continue until April.

Auctioneer Ben Rogers Jones added: “There are some pieces beyond estimate, and others which are virtually worthless…it’s up to you to work out which are which, as we don’t really know ourselves.

“Though as a whole , with the provenance of Plas Teg, it’s unlikely that another collection like this will ever come on the market again in our lifetimes.”