In 2020 the building was placed into receivership as it was undergoing a multi-million renovation.
It had been bought by a couple who hoped to turn it into a luxury hotel when they took it over in 2016, after the collapse of a previous wedding venue venture in 2013.
The mansion was sold in 2020 after a failed attempt to turn it into a luxury hotel.
It was put back on the market in 2024 by its Manchester-based developer owner David Savage and his company for £2m but it is believed to have recently been taken off the market.
The surrounding park at Plas Glynllifon, boasting eight miles of paths, is also listed and its website on Wednesday, external was still inviting visitors to “immerse yourself in history, culture and nature… [at] one of North Wales’s finest parks”.
Hughes said the investigation was still ongoing and asked the public to avoid the home to avoid any risks.
“We uncovered a grow, which was on the top floor of the building. We estimate around 12 rooms with grows in them and they were fairly mature plants.
“There’s lots of information to process today and lots of forensic work to consider, and lots of other digital matter that we are looking at.
“I’m quite confident we can get to a point where we can make some arrests.
“Clearly, the electrics are being manipulated and lots of water supply being diverted inside and the property itself is in various states of disrepair.”