The Ministry of Justice has said that Gloucester Prison and Shepton Mallet in Somerset is one of six prisons that will close in England under plans to build a so-called super-prison.
Shepton Mallet prison is the oldest working prison in the country.
Some 2,600 offenders are held at the prisons targeted for closure, plus three sites which will be partially shut down.
Prisons at Bullwood Hall, Canterbury, Gloucester, Kingston, Shepton Mallet and Shrewsbury will close, while Chelmsford, Hull and Isle of Wight will see some accommodation reduced.
A feasibility study on what would be Britain's largest prison in London, the North West or North Wales, holding more than 2,000 prisoners, is also to begin, the Ministry of Justice (MoJ) said.
More top news
In horrendous conditions at the Rec, Gloucester get hard-fought win over local rivals Bath at the Rec.
Catwalk ready - a meningitis survivor, prepares to perform for the South West's biggest fashion show.
The Atlantic Jet Stream brings a yellow warning to the South West. There's the prospect of heavy rain and strong winds on the way.