Police made 20 arrests after a series of dawn raids linked to the investigation into the theft of Chinese artefacts and a rhino horn last year.
The raids, which took place on September 10, were connected to six burglaries over a four-month period - three at Durham University's Oriental museum, one at Gorringes saleroom in East Sussex and one each at the Norwich Castle and Fitzwilliam Museums, the latter in Cambridge.
Eight people have already been convicted and jailed for their roles in the break-ins.
The latest raids, which took place in London, Essex, Sussex, Cambridgeshire, West Midlands and Northern Ireland, involved 26 police forces and the Serious Organised Crime Agency.
Nineteen people were being held on suspicion of conspiracy to commit burglary, while a 54-year-old woman was arrested on suspicion of perverting the course of justice and assisting an offender. All of those people have now been released on bail.
Chief Constable Mick Creedon, the Association of Chief Police Officers' lead for serious organised crime, was reported by the BBC as saying: "Many of the stolen Chinese artefacts are still outstanding and a substantial reward remains on offer for information which leads to the safe return of those precious items."
The 18 Fitzwilliam items stolen were mostly Ming and Qing dynasty jades and had been part of the museum's permanent collection for over 50 years. A PDF of these items appears in ATG's report of the theft.
Police recovered the objects stolen from Durham's Oriental Museum shortly after the burglary. An 18th century jade bowl and a porcelain figure were found in a field in the Brandon area, a few miles to the south-west of the city.