As widely reported last week, detectives believed the Johnsons, based at a caravan park in Evesham, Worcestershire, were at the centre of a crimewave affecting in the South of England for 20 years.
They carried out a string of raids on stately homes in Wiltshire, Oxfordshire, Berkshire and Worcestershire between April 8, 2005 and October 13, 2006. They spent weeks staking out properties and used 4x4 vehicles to ram heavily bolted gates.
Their plunders included what has been called Britain's biggest-ever domestic burglary in February 2006, the £30m raid on Ramsbury Manor, Wiltshire, the 17th century home of property tycoon and discerning collector Harry Hyams.
The Johnsons also raided Warneford Place, the former home of James Bond author Ian Fleming and now the home of Formula One advertising tycoon Paddy McNally, and twice struck Woolley Park, the Berkshire country home of Lord Lieutenant of Berkshire Sir Philip Wroughton.
Three Johnson family members also stood trial for conspiracy to burgle Waddesdon Manor, near Aylesbury, Buckinghamshire. In 2003 a masked gang stole £5m worth of rare snuffboxes from the National Trust property that have never been salvaged, but the case collapsed after the judge ruled that certain evidence could not be included.
Detectives from five police forces took part in the investigation codenamed Operation Haul. Two months after the Ramsbury raid, detectives found items from the haul in black bin bags in an underground bunker in a field owned by an associate of the Johnsons near Stratford-upon-Avon.
The items - some of them damaged - amounted to one third of the items taken at Ramsbury but represented only a small fraction of the total value.
The men were convicted of conspiracy to commit burglary in January, following a month-long trial at Reading Crown Court - but the case can only be reported now because another case involving one gang member, Daniel O'Loughlin, was pending.
Ricky Johnson, 54, was jailed for eight years, his sons Richard 'Chad' Johnson, 33, and Albi Johnson, 26, were jailed for 11 years and nine years respectively, his nephew Daniel O'Loughlin, 32, and his daughter's partner, Michael Nicholls, 29, were jailed for 11 years and ten years respectively.
Aside from the Ramsbury breakthrough, there have been few leads in recovering the stolen objects. Passing sentence, Judge Christopher Critchlow said: "Little of the property has been recovered and is no doubt well hidden in the countryside or passed on for disposal."
So far just three additional items have been found.
In February 2007 a West Country auctioneer notified the Art Loss Register after becoming suspicious of a late entry of a Vulliamy bracket clock. It emerged that the clock had come from Woolley Park. This also led to the recovery of a mantel clock by Gibson of Newbury. The consignor, who had connections to the Johnson family, was charged.
A 17th century portrait of Cardinal Infante Ferdinand by Abraham van Diepenbeck, stolen from Ramsbury, was also found in May this year.