A worker is in a critical condition in hospital after being pulled from a lake on the Queen's Sandringham estate in Norfolk.
Emergency services were called to the retreat at about 1.30pm yesterday after reports that an estate worker, in his 30s, had fallen into the Lower Lake while operating a ride-on lawn mower.
It is understood the Queen was at Sandringham on a private visit less than an hour later.
A spokesman for Norfolk Police said: "The man was retrieved from the water and was taken to Addenbrooke's Hospital by air ambulance for treatment. He is currently described as being in a critical condition.
"Police and the Health and Safety Executive are carrying out a joint investigation into the incident."
Lower Lake is next to the Estate Office, also known as York Cottage.
The converted house was the residence of King George V.