Three people were arrested and two prisoners taken to hospital following a riot at Bedford jail.
Police have confirmed officers from Bedfordshire, Cambridgeshire, Hertfordshire and Essex were needed to deal with the disturbance which broke out just before 5pm on Sunday.
Three men - aged 39, 37 and 26 - have been arrested on suspicion of committing offences under the Prison Security Act 1992. They remain in police custody.
Two prisoners were taken to hospital during the incident - one had become unwell and another suffered minor injuries during the riot. Both have been treated and returned to prison.
More than 200 prisoners have been shipped out of HMP Bedford - including 50 riot "ringleaders" - as two wings are said to be out of action.
A prisoner released from Bedford jail just a week ago says conditions inside are "a joke" and Sunday's riot was "a long time coming".
Inmates from Bedford jail will be transferred to other prisons "throughout the day" following Sunday's riot, a prison official said.