overcrowding

Their release was part of an emergency government scheme to help ease overcrowding in prisons.

Migrants are supposed to be held there for 24 hours, while officials carry out security and identity checks, but overcrowding has sometimes led to people being forced to stay on the site for weeks.

That provided some relief for prisons in the face of overcrowding but populations have since continued to rise.

The shift comes as questions about sustainability, overcrowding and commercialisation reshape mountaineering.

President of the Prison Governors' Association Tom Wheatley said successive governments have failed to deliver the prison spaces needed to deal with dangerous overcrowding.