HE called it a “once in a lifetime” discovery.

And Winchester City Mill employee Ric Weeks simply couldn’t believe it when he stumbled upon the small watercolour.

Depicting the mill, it is by one of Britain’s best-loved and well known artists, JMW Turner.

Mr Weeks, assistant manager at the National Trust property, said: “It’s a once in a lifetime thing. I was absolutely dumbfounded because I know every image of the mill there is. To see one I did not know of was just amazing. I thought “something’s gone wrong here. This has somehow escaped my knowledge.

“I was just browsing through the Tate's Turner collection as I had heard that a lot of their collection had been digitalised.

“To find an old painting of the mill is fantastic, but for it to be by Turner is unbelievable. The people at the Tate have been really helpful and we have arranged for a high quality print of the painting to become part of the mill’s permanent exhibition for our visitors to enjoy.”

The watercolour had been bequeathed to the nation over 150 years ago, but was unknown to the National Trust until now.

Dated 1795 and painted in grey and brown wash, the painting forms part of Turner’s Isle of Wight Sketchbook, from his tour of the south coast when a student of the Royal Academy.

Rob Humby, council deputy leader, would be keen to see the artwork lent to city for public display. “It is something we would love to be able to do.”

A spokesman for the Tate was unable to say how often the sketchbook is accessed, but said they would certainly consider loaning it to the city.

“I have not had a chance to see the actual original yet, but that’s something that’s going to happen soon.

“It would be fantastic if they loaned it to Winchester, but from my experience with the trust, I think it would be quite unusual for them to loan it to the city. But if it did, we would love to see it here,” Mr Weeks said.