A prison recently described as "teetering on the edge of a major incident" has been placed in special measures.
The Ministry of Justice (MoJ) said it had now placed it in special measures.
It added it was "considering a range of options" to help it improve.
Body-worn cameras have been introduced at the prison, as well as the installation of additional CCTV and extra staff have been recruited, the MoJ said.
Since the IMB inspection, the governor has also introduced changes to the regime "which has resulted in a more stable environment for staff and prisoners", it added.
It was not specified what the changes were.
Winchester MP Steve Brine said: "It's about facing up to the clear challenges Winchester has and that has to be right.
"I am speaking to the new minister and will be in with the governor soon to scrutinise their turnaround plan."
The IMB report said the Victorian jail was understaffed and had "inadequate" facilities.
Inspectors found some inmates were locked up for at least 23 hours a day in small, shared cells and likened its separation unit to an "unpleasant dungeon".
Levels of violence were also described as "high", with about 17 attacks by prisoners recorded every week.
The report also said the building was deteriorating and had limited disabled access.
However, it did note the "positive impact" the arrival of a new governor in August 2016 had provided.
An MoJ spokesman said it was recruiting an extra 2,500 extra officers across its prisons and had put new security measures in place to tackle drones, phones and drugs.