There are 100 spaces left in men’s prisons in England and Wales, it is understood.
The system, already in the middle of an overcrowding crisis, is normally under greater pressure after a bank holiday weekend, which eases once courts reopen.
On Friday magistrates were told to delay jailing criminals as the number of people in prison hit a new weekly high.
The prison population then stood at 88,234, the highest end of week number since weekly data was first published in 2011.
Earlier this month a UK Ministry of Justice (MoJ) spokesperson said that more than 500 places will be made available in the coming weeks.
They added: “The new Government inherited a justice system in crisis and has been forced into taking difficult but necessary action to ensure we can keep locking up dangerous criminals and protect the public.
“Staff across the whole criminal justice system are working incredibly hard and the Government will continue to support them before the changes come into effect on September 10.”
Plans are in place to release some inmates early to relieve overcrowding, and emergency measures have already been brought into force in the north of England to allow prisoners to be held in police cells.
There is considerable concern among justice figures about what could happen over the coming weeks prior to prisoners being freed early, the PA news agency understands.
Last month, UK justice secretary Shabana Mahmood announced plans to cut the proportion of the sentence inmates must serve behind bars from 50 per cent to 40 per cent, as the MoJ said violence and self-harm in prisons had risen to “unacceptable” levels as overcrowding pushed jails to the “point of collapse”.
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.
