FOR nearly a century, a vault beneath a historic Brighton house converted by renowned architect Edwin Lutyens into a “palace” for the aristocratic mother of the controversial writer Vita Sackville-West has lain hidden under a slab of concrete.

Filled over the years with builders’ rubble, it has now been uncovered and next year will be transformed into a unique subterranean living space.

“There will be nowhere else like it in Brighton,” said Ian Barr, who jointly owns the Grade 1 listed Regency house at 40 Sussex Square with his sister Susan Jacobs. “It’s unique and it’s very exciting.”

The vault was uncovered when the owners began some clearing out around six years ago –and then it was followed by another exciting discovery.

As part of the clearout, a cupboard under the stairs inside the house was unlocked for the first time in years, and stuffed inside were Lutyens’ original drawings for his plans for the conversion.

“We had known the vault was there, filled with builders’ rubble and other material,” said Mr Barr. “But we hadn’t realised the significance of it until we found the drawings. We couldn’t believe it. They had been stuck away under the stairs and it was only because of the clearing out that we found the drawings.”

He added: “We will be retaining all of Lutyens’ features in the vault, including exposed brickwork. It will be an amazing living space.”

Sussex Square formed the main part of the development of Kemp Town during the 1820s, and Number 40, originally designed by Brighton Regency architect Charles Busby, was built around 1823. Famous residents of the square would include Thomas Read Kemp, who financed the creation of Kemp Town, the author Lewis Carroll and Louis-Phillippe, the exiled king of France.

Victoria, Lady Sackville-West, the illegitimate daughter of the 2nd Baron Sackville and a Spanish dancer, bought two houses in Sussex Square in 1918 following her separation from her husband, her cousin, the 3rd Baron Sackville. She spent £50,000 - the equivalent of millions of pounds at the time – turning them into a single palatial home with the help of her friend Lutyens, with whom she enjoyed a relationship that was “closer than just friends”.

The vault underneath the house, which was converted into flats and renamed Sussex Mansions in the 1930s, was designed to lead Lady Sackville-West through to an underground road tunnel and into an ornamental garden on the other side of Bristol Place, designed by famous horticulturalist Gertrude Jekyll.

“We don’t know whether the garden was ever built,” said Mr Barr. “We can’t find any evidence that it was created but we plan to re-create a garden, which will be smaller than the original but along the lines of the one designed by Gertrude Jekyll for the subterranean living space.”

Lady Sackville-West, a close friend of the sculptor Auguste Rodin, moved into the house in 1922, along with seven van loads of furniture. Her daughter, Vita, remarked in her memoirs that her mother had bought “a hideous house in Brighton” and had spent hundreds of thousands of pounds remodelling it into something worse. According to researcher Andrew Doig, writing on the website, “her gardens were planted with tin and china flowers... she built a staircase of imitation books with joke titles and was delighted to see visitors try to pocket a half crown painted on her doorstep... for housewear, her favourite garb was a cheap flannel nightgown, fastened by an emerald and diamond brooch, from which hung a sixpenny police whistle”.

Lady Sackville-West lived there for just a year, daunted by the cost of running such a huge property, and when she moved out to a house in Roedean, also designed for her by Lutyens, she held a seven-day sale of her belongings, which included sculptures by Rodin and Jacob Epstein and a 42-stone diamond necklace.

The vault was sealed under concrete after the house was turned into flats because it was no longer needed. Brighton and Hove City Council has now given planning and listed building permissions for its refurbishment as well as the new garden inspired by Gertrude Jekyll’s original plan.

The plans were drawn up by estate agent Savills in Petworth, whose architecture department, headed by Ewan Stoddart, worked on the plans with the council’s conservation department.

Mr Stoddart, who specialises in heritage-led projects, said: “It has been a joy working on this. It was a tricky site to get to grips with and we gave it our best shot. Although I work in Petworth, I’m a Brightonian and I love the history of the city, which is considered to be the Las Vegas of the Regency period.

“Lady Sackville-West spent a fortune on this house, and got the go-to architect of the 1920s and 1930s to redesign it. She went for it but she exceeded her budget in a Downton Abbey kind of era, where that kind of setup was really in decline.

“When we got hold of Lutyens’ original drawings, we found out there was supposed to be a pergoda."

“Thanks to a thorough understanding of the heritage and the architectural significance of this long forgotten space, we were able to submit a robust application for the vault, subsequently gaining planning permission.”

Work is expected to begin in the early or middle part of next year.