A police team including forensic archaeologists will scour a farm north of London for the third time after one of the men convicted of the kidnapping reportedly revealed the location of victim Muriel McKay’s body.

London’s Metropolitan Police said a no-fly zone would be in place over Stocking farm near the town of Bishop’s Stortford to “protect the integrity of the search and dignity for the deceased should remains be found”.

Brothers Nizamodeen and Arthur Hosein kidnapped McKay, then 55, in 1969 for a £1 million ransom – the equivalent now to £14 million – thinking that she was Murdoch’s second wife Anna.

The brothers had followed Murdoch’s Rolls-Royce unaware he had lent it to his deputy Alick McKay, Muriel’s husband.

They were convicted of murder and kidnap after a 1970 trial, but denied killing the newspaper executive’s wife and refused to reveal where she was buried.

Nizamodeen served 20 years in prison and was then deported to Trinidad, while his brother Arthur died in prison in the UK in 2009.

Nizamodeen Hosein, however, last December gave McKay’s family a sworn statement confirming the location of the body, telling them he wanted his “conscience to be clear”, the Murdoch-owned Times newspaper reported.

He has previously claimed McKay collapsed and died while watching a television news report about her kidnapping.

McKay’s grandson, Mark Dryer, told BBC television the focus of the latest search would be an area behind a barn that has not been dug before.

“If we don’t find her it will be a disappointment, but it won’t be unexpected. But without searching for something you’re never going to find it,” he said.

“We haven’t dug behind the barn, no one’s ever dug behind the barn,” he added.

The search is expected to take around five days but could be extended.