Chris McHugh, in Woodstock

OPUS CONSERVATION A young man wearing a high visibility jacket, black latex gloves and an industrial face mask gently dabs a large painting above his head with a cotton bud-like instrument. The painting is a historic wall painting appearing to show two women under a fishing netOPUS CONSERVATION

The Great Hall ceiling painting by Sir James Thornhill is one of the two paintings being restored

Two 18th century masterpiece paintings at risk from a damaged palace roof are being protected by a new £1 million conservation project.

Blenheim Palace said the works were at risk of being “lost forever” if the project was not carried out.

The paintings being restored include the Great Hall ceiling work by Sir James Thornhill, from 1716, and Louis Laguerre’s paintings of the Battle of Blenheim located in the Saloon.

The scheme forms part of a £12 million restoration of the palace’s roof, set to finish in 2026.

CHRIS MCHUGH/BBC A large circular white and brown water damage stain is visible covering decorative stonework with flower shapes. Large white drip stains can be seen underneath. CHRIS MCHUGH/BBC

Water damage from the leaking roof now lies just metres away from the ceiling painting in the palace’s Great Hall

The palace said a combination of “age, climate change and penetration from rainfall” had led to the declining state of the roof, attic timbers and ceilings.

Work on the roof and paintings is running concurrently, which the palace described as the “most ambitious undertaking” in its history.

The BBC was shown water damage to the Thornhill painting’s surrounding stonework being painstakingly cleaned by conservators.

Kelly O’Driscoll, head of Built Heritage at Blenheim Palace, said the painting had been damaged by years of dirt and water ingress.

“We could end up losing this painting… it’s a race against time to get it looked after”, she said.

CHRIS MCHUGH/BBC A wide image of a large baroque painting on the ceiling of the great hall in Blenheim Palace, depicting several historical figures in a grand ballroomCHRIS MCHUGH/BBC

Thornhill’s painting was conceived as a celebration of the 1st Duke of Marlborough’s military successes

Lizzie Woolley, director of OPUS Conservation, said damage was currently limited to a metre away from the edge of the ceiling painting.

“If you leave it and the roof continues to deteriorate, you risk it coming closer in and damaging this masterpiece.”

The year-long project is funded by The National Lottery Heritage Fund and the Blenheim Foundation.

The palace said the work would include new studies of the paintings and hands-on training for the “next generation of heritage professionals”.

The palace said the Tate, The Courtauld Institute of Art and the University of Oxford would all contribute to the research.

Carmel Jane An aerial view of the ornate roof of Blenheim Palace. Statues are visible at the top, and the brickwork is of a sandy orange colour. Well-tended parkland is visible in the background. Carmel Jane

The works are part of a £12 million restoration of Blenheim Palace’s roof