John Hardy, 42, who leases the house from the city council, said no-one noticed the paintings' great value and just accepted them as part of the general collection.

It is an absolutely excellent find for the whole country

John Hardy

"People just took them for granted and didn't notice them.

"But when we came to getting them insured by Sotheby's, they spotted them," said Mr Hardy.

"It is an absolutely excellent find for the whole country.

"We first of all thought they were copies, quite frankly.

"We couldn't believe they were real."

The paintings were found in a conference centre

The paintings are owned by a trust but were on loan to Mr Hardy who had found them in a Devon barn when he was doing some historical research into the house and the Southwell family who once owned it.

Looking for paintings for the house led him to the Hilda Inge Will Trust which mentioned two lost Canalettos and his detective work took him to the barn.

Auction house Sotheby's is now keeping the paintings in storage in London.

Although the potential value of the paintings has not been disclosed, auction house Christie's said they have sold good-condition Canalettos for up to �11m in the past.