The Chief Inspector of Prisons has laid bare his concerns about overcrowding, safety and drug use in Welsh jails.
Peter Clarke told MPs of how there had been 'some deterioration' in the quality of prisons and said HMP Swansea had failed to make recommended improvements.
Describing its response as 'particularly poor', he said: 'I think it was probably the worst I’ve seen anywhere.'
Mr Clarke also warned of 'slight deterioration' at HMP Cardiff and HM Prison Parc in Bridgend.
All three prisons suffered from overcrowding but he said Swansea was the 'most extreme'.
Figures for December show that the prisons had more inmates than the 'certified normal accommodation' (CNA) levels.
- Swansea has a baseline CNA of 268 inmates but housed 411.
- Cardiff had 706 inmates instead of 539.
- Parc Prison had 1,736 despite a normal level of 1,559.
Speaking to the Welsh Affairs committee, Mr Clarke made the case that poor conditions make it more likely people will use drugs.
A Prison Service spokesman said the prison continues to work to 'implement the recommendations of the Inspectorate'.