Ministers have activated emergency measures to ease prison overcrowding as more rioters are sentenced for their role in the recent unrest.

The longstanding measures, known as Operation Early Dawn, allow defendants to be held in police cells until prison beds become available and could mean their court dates are delayed or adjourned at short notice.

The system was activated on Monday morning and means some defendants across the north of England waiting for a court appearance will be kept in police cells until prison space is available.

The government said that its action to “tackle violent thuggery on our streets” has “exacerbated longstanding capacity issues in our prisons”.

James Timpson, the prisons minister, said: “We inherited a justice system in crisis and exposed to shocks. As a result, we have been forced into making difficult but necessary decisions to keep it operating.”

He said the emergency measures would help “manage the pressure felt in some parts of the country”.

He added that anyone who posed a risk to the public “will not be bailed” and police’s ability to arrest criminals will not be affected.

Nev Kemp, of the National Police Chiefs’ Council, said: “We are working closely with criminal justice system partners to manage demand in the system and ensure that the public are safe. Policing will continue to arrest anyone that they need to in order to keep the public safe, including policing protests and events and ensuring that people are arrested as expected.”

Mark Fairhurst, the national chair of the Prison Officers’ Association, said on Sunday that the measure risked “clogging up police cells” and he blamed rioters for increasing the pressure on prisons.

Fairhurst told BBC Radio 4’s Broadcasting House on Sunday: “Last week we had the biggest influx of new receptions I’ve seen for quite some time. We had 397 new receptions. As of Friday we only had 340 spaces left in the adult closed male estate, which is feeling the most pressure.

“I wouldn’t be surprised if at some point tomorrow morning the Ministry of Justice would announce that Operation Early Dawn kicks in to play at some point next week, probably Tuesday onwards.

“The pinch points at the moment are the north-east and the north-west, so it’s likely that if you commit an offence in those areas you will be carted 100, 200 miles away from home to serve your sentence because there’s simply very few spaces.”

Operation Early Dawn is a contingency measure that has been used for very short periods – usually no longer than a week – to manage immediate, localised, pressures on the prison estate. It steps up coordination between police stations, the Prison Service and the courts to make sure nobody is taken to the courts until the Prison Service can guarantee a space for them should they be remanded.

In May, Operation Early Dawn was triggered in London and north-east England before being rolled out across England after concerns over prison overcrowding. It meant that defendants in police custody remained there and were not transferred to magistrates courts for bail hearings in case there was no space in jail cells for those remanded into custody.

During the same month, police were instructed to consider making fewer arrests because of the lack of space in prisons.

The scheme is overseen by the Ministry of Justice (MoJ) and therefore could be used across England and Wales. On this occasion, the measure will be put in place in the north-east England and Yorkshire; Cumbria and Lancashire; and Manchester, Merseyside and Cheshire regions.

Last month, the MoJ said violence and self-harm in prison had risen to “unacceptable” levels as overcrowding pushed jails to the “point of collapse”.

The justice secretary, Shabana Mahmood, announced plans to cut the proportion of the sentence inmates must serve behind bars from 50% to 40%. The temporary move – which does not apply to those convicted of sex offences, terrorism, domestic abuse or some violent offences – is expected to result in 5,500 offenders being released in September and October.