The discovery was made this morning at Plas-yn-Pentre, an Elizabethan house near the village of Trevor, between Llangollen and Wrexham, which has been empty and for sale for some time.

The cannabis factory, which was described by a police officer at the scene as the "most professional" she had ever seen during her career, was found by the house's property-developer owners who had not been there for several weeks.

It is thought that the culprits have caused some damage to the historic building as well as reconnecting the electricity and water supply, which had been disconnected while the house was empty.

Police are now searching for two people, a man and a woman, both described as being "of Oriental appearance" who were seen leaving the house.

Sergeant Mavis Evans said: "Police received a call from the owners of the property early this morning to say that two people had been seen acting suspiciously at Plas-yn-Pentre. Once officers arrived we discovered that a cannabis factory had been set up in the building. There are numerous plants in situ at various stages of growth on all three floors of the house."

Police also found a large quantity of compost bags and growing apparatus in the building.

Sergeant Evans added: "We would like to trace the whereabouts of two people - one male, one female - both described as being of Oriental appearance who were seen leaving the site."

Plas-yn-Pentre's owner, John Sumnall, a property developer from Staffordshire, bought the house to renovate the adjacent barns but he and his workers had been asked to move off the site after bats were discovered.

Because of this and a family bereavement, John had not been back since and had no knowledge that anyone had broken in.

When the estate agent contacted him about a viewing, John called his friend and business partner, George Batty and asked him to go to Plas-yn-Pentre with a key for them.

George said: "I came down this morning after John called and I noticed that there was a padlock on one of the gates but it was open. I walked around to the house and saw that one of the windows had been boarded up which I knew we hadn't done."

George feared that squatters had moved in and immediately called the company secretary to let them know.

He continued: "When I got closer I could hear someone inside. I shouted and two people bolted out of the door on the other side of the house. I was on the phone to the secretary so I told her to call the police. One of them ran through a metal fence to get away. I chased them for a while but I decided to go back to wait for the police."

Anyone with any information about the cannabis factory or who has seen anybody acting suspiciously in the area is asked to contact North Wales Police on 0845 6071001 (Welsh line), 0845 6071002 (English line) or Crimestoppers on 0800 555111.

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