Urgent repair work under way at 15th Century house

The water in the moat helps to support foundations at Oxburgh Hall in Norfolk

An urgent conservation project is under way to preserve a manor house built more than 500 years ago.

Water levels in the moat at Oxburgh Hall, near Swaffham in Norfolk, became unusually low due to leaks last year and then a sinkhole appeared on a lawn.

A watertight enclosure called a cofferdam has been installed to allow contractors to repair the moat as part of work costing £196,000.

Donna Baldwin from the National Trust said it was a "delicate balancing act" to keep water levels high enough to protect the building's walls without flooding the gardens.

"If the water drops too low, the brickwork is exposed, which has an impact on the structural integrity of the hall itself," she said.

Workers are expected to remain at the site until the end of June and will also repair the sluice and culverts.

The moat is fed via an underground channel from the River Gadder, with culverts allowing water in and out.

The sluice gate controls the amount of water draining out of the moat and back to the Gadder.

The Oxburgh Estate is owned by the National Trust but has been the family home of the Bedingfelds for more than 500 years, and they still live in private apartments at the hall.

Moat repair work at Oxburgh Hall in the early 1900s