By Dominic Casciani
Home affairs reporter, BBC News
The government says the officers are acting illegally
Thousands of prison officers have ended their strike action after a surprise walkout early on Wednesday. Why did they walk out and what effect is it likely to have had on jail life?
What action did prison officers take?
On Wednesday morning, members of the Prison Officers Association (POA) said they were staging a 24-hour strike over pay and conditions. The strike began at 0700 BST and ministers immediately said the move was illegal. It was the first national walkout by the association in its 68-year history.
The association has some 28,000 members in 129 English and Welsh prisons and the BBC understands that all of them suffered disruption. The strike did not however affect jails in Scotland or Northern Ireland.
Whom does the POA represent?
The POA represents staff across the prison service from store men and night patrols to principal officers responsible for managing entire wings. The association also represents officers on the first two governor rungs and some staff in the three maximum-security special hospitals. POA members in private sector prisons have separate agreements that are not part of the dispute.
Did the POA act legally?
The Ministry of Justice successfully sought a High Court injunction against the strike within hours of it beginning. The injunction prevents the POA from "inducing, authorising or supporting" industrial action disrupting prison operations.
If executive members of the POA refused to comply with the injunction they would be in contempt of court and liable for prison themselves. Striking officers outside at least one prison were given a print-out saying they too would face legal action.
Is it lawful to strike?
In 1994 the then Conservative government banned prison officers from striking. Labour repealed the ban and introduced a voluntary "no strike agreement" aimed at improving volatile industrial relations.
In June, the POA told ministers they intended to pull-out of the agreement - but legally they are required to give 12-months' notice.
But at the same time, the Prison Service, struggling with a record population, has signalled that it is not prepared to allow the POA to call the shots. It has already been to court in the past year over a POA call not to sign overtime contracts.
Earlier in August the POA said its national ballot on pay and conditions found 87% of members endorsed industrial action up to and including a strike.
What kind of impact did the walkout have?
Prison officers are not only key to the safe and secure running of jails, they effectively oil the wheels of great parts of the criminal justice system.
PRISON OFFICER SALARIES
Auxiliary staff: £13,318
Night patrol: £14,084
Entry officer min: £17,744
Prison officer: £27,530
Senior officer: £29.371
Principal officer: £31,913
Recommended top pay in posts as of April 2007. Source: Office for Manpower Economics
A normal day begins with prison officers unlocking cells for breakfast.
But Mark Leech, founder of the Prisons Handbook and a commentator on the penal system, said there would have been chaos this morning.
"The prisoners who got fed first thing will be the lucky ones," said Mr Leech.
"There will be some who may not be fed until late afternoon because a dozen or so governors will be trying to run a controlled unlocking with just two or three prisoners at a time being allowed out. I won't be surprised if some are still being fed at 3pm."
And how will the strike have affected the rest of the day?
Between 0900 and 1100 inmates would have been expected to attend various courses, classes, workshops, counselling sessions and drug treatment plans. All of these sessions are crucial to the life of prisons and the chances of an inmate being released by a parole board.
But a prisoner does not just leave the breakfast table to go off to a session of their choosing. They are escorted by officers - and with the POA on strike, governors alone did not have the manpower to get inmates to the right places.
The only answer was to keep the prisoners locked in cells. Later in the day there would normally have been free-association periods and exercise. These too were halted in affected prisons. Lunches in many institutions are understood to have been restricted to a few sandwiches eaten in locked cells.
What about contact with the outside world?
Nobody can come in or out of a prison without officers unlocking doors and processing arrivals at reception. This means that visits were off. Mr Leech said that it's not unusual for elderly relatives to have made a long trip from one end of the country to another for a rare visit. They would have been turned away.
And the courts?
Private contractors escort prisoners to and from courts - but they require a prison officer to oversee the transfer of the individual from the jail to the waiting van.
Where prison officers were striking, prisoners could not leave for court - and those being sentenced have not been received. Not all court work will grind to a halt - but many courts and trials will be affected with a massive cost to the public purse.
What happens if someone cannot be transferred to prison?
The government already has in place Operation Safeguard, an emergency procedure to use up to 400 police cells as part of measures to ease prison overcrowding.
What led to this situation?
For 20 years relations between the Prison Service and the POA have been difficult, particularly over the private prisons agenda and overcrowding. But the key issue has been pay.
Earlier this year the independent prisons pay review body recommended salaries ranging from £12,000 for auxiliary staff to almost £32,000 for principal officers. Most prison officers start on about £17,700. The top pay for a governor is approximately £78,000.
The government has implemented the recommended 2.5% pay award in two stages. The POA says this reduces its value to 1.9% - below inflation.
The union says fresh talks with the government are now set to take place on Friday.