Leading conservationists have expressed their outrage over the sale of historic marbles from the grade II* listed Ince Blundell Hall, which they claim could set a dangerous precedent.

A group of Augustinian nuns has applied to Sefton council to sell 102 classical sculptures contained as part of the estate’s Pantheon and Garden Temple, which they claim are at risk. The move has been backed by English Heritage “to prevent further deterioration and because of the current threats of theft and vandalism”.

Architectural historian John Harris said: “Obviously listed building consent had to be obtained through the planning department of Sefton District Council.Outrageously the English Heritage director, Henry Owen-John gave consent, a most ignorant decision, for in so doing he smashed through all the current enshrined legislation to prevent the removal or heritage works of art from their fixed positions.”

Harris also signed a letter written by Charles Sebag-Montifiore, joint secretary of the Society of Dilettanti, to the Daily Telegraph which said the sale would be an “unwelcome precedent” and called on the council and English Heritage to work to keep the collection intact.

And in a letter to Sefton Council Will Palin, secretary of Save Britain’s Heritage, said the sale could set a precedent “prompting many other owners to sell fixtures and sculptures not housed in ideal climatic conditions”. Tim Knox, director of John Soane’s Museum, has also spoken out against the sale.

Meanwhile, a question has been raised about the ownership of the marbles, which form part of the building – now a nursing home.

“The heir of [Henry] Blundell who assembled the collection donated all other sculptures at the building to Liverpool museums,” said Palin. “Legal advice is now being sought to prove ownership of the marbles – they can’t sell them if they don’t own them.”

The council is expected to make its final decision in January.

English Heritage was unavailable for comment.