UNIQUE handwritten letters and watercolours relating to unfinished gothic masterpiece Woodchester Mansion have been discovered in a plastic bag in an Amberley attic.

Chairman of the Woodchester Mansion Trust, Stephen Davis told the SNJ: ""These things have turned up in a local village 150 years later. They tell us an untold part of our history. They are remarkable."

The precious documents include an 1878 letter from mansion architect Benjamin Bucknall to Squire Leigh, son of William Leigh, the man who commissioned him to create the building.

In it the architect, who ended his career building villas in Algiers, writes poignantly: "There's nothing more sad to the site than an unfinished work and it is even more forlorn than ruin of a building which has served its purpose...

"Believe me that these remarks are only suggested by a sincere interest in a place associated with many happy days. Most truly yours, Benjamin Bucknall".

"I don't doubt these were the last words he ever wrote about the mansion, which was his life's work," said Stephen.

He describes Bucknall as the "undiscovered architectural genius of Stroud," and the mansion as "his greatest achievement".

Bucknall was third in a line of architects to whom William Leigh offered the commission to replace old Spring Park after buying the 1,000-acre Woodchester Park estate in 1845. First up was the great Gothic revivalist A W Pugin but his plans were dismissed as too expensive.

The collection contains three of his letters to Leigh dated 1845.

Next came Charles Hansom, of Hansom cab renown, but it is thought his chances were scuppered by a disagreement with Leigh. The find includes two letters from Hansom.

And so it was that his 21-year-old assistant Bucknall, from Rodborough, was handed the commission.

After Leigh's death in 1873, the family turned to James Wilson, Cheltenham College architect, for a new design

A letter from Wilson to the Leighs bemoans the position of the unfinished mansion and includes alternative plans and an artist impression of what he has in mind.

The correspondence is a revelation to the trust. "We didn't know anything about Wilson," said Stephen. "All these guys were pitching for work. The Leigh family must have been fed up with architects by the mid 1870s."

The breath-taking collection, which also includes two surprisingly well preserved watercolours of Spring Park, was discovered in the attic of Margaret Gardner's Amberley home earlier this year.

She had been going through papers belonging to her late father Bert Smith. She said: "I found no end of father's papers and then these letters and I suddenly realised what I had got.

"When you see 1846 on a letter you think 'Wow, what have I got here?'" Her father worked for Gloucester mental hospital Barnwood House Trust, which bought the mansion from William Leigh's granddaughters Blanche and Beatrice in 1938 with a view to a conversion that never took place.

"My father took charge of looking after the mansion and the park," explained Margaret. "During that time he got to know the Leighs. I can only assume that during that time they gave the documents to him for safe-keeping."

It is hoped the documents will in future form part of a mansion archive and information centre.

In the meantime, more people are being sought to help run the mansion. To volunteer call Judith Silverwood on 01453 755640 or Pat Wollaston on 01453 873509.