The protest started on Monday evening
A rooftop protest at a jail has came to a peaceful end after the remaining inmates ended their demonstration.
Twenty prisoners occupied the roof at category C Wealstun prison, near Wetherby, on Monday night breaking windows and climbing up drainpipes and ledges to the roof.
After 19 hours on top of the roof of C block, four of the prisoners came down followed shortly afterwards by two more brought down in a crane by police negotiators.
The final inmates came down in small groups through the night until the final six surrendered peacefully at 0306 BST - more than 30 hours after their protest started.
Urgent action must be taken to reduce the current prison population before further disturbances occur
Colin Moses, Prison Officers' Association
An internal investigation has been launched by the prison.
Colin Moses, chairman of the Prison Officer's Association blamed prison overcrowding for the protest.
Mr Moses said: "It appears once again that overcrowding has resulted in a serious situation in one of our prisons.
"Urgent action must be taken to reduce the current prison population before further disturbances occur."
He said staff at the jail blamed the incident on pressure arising from accommodating overflow from HMP Liverpool and HMP Manchester.
But a Prison Service spokesman said it may have been sparked by a series of complaints about changes to the jail's exercise regime.
Tony Goodall said: "Exercise has changed from last thing in the morning to the first thing in the morning."
"The exercise field is now part of a building site so we've lost some space.
"We are now looking at improving facilities so the prisoners get decent exercise."
The jail, which opened in 1965 on the site of a former munitions factory, has 600 inmates.