The new coronavirus strain and a rapidly rising number of infections in prisons across England and Wales is a "public health emergency unfolding before our eyes," the shadow justice secretary has warned.
Labour MP David Lammy said it was vital that ministers "act urgently" to prevent the virus from spreading further in jails - or risk preventable deaths.
"We're not condemning our prisoners to death in this country, but for some prisoners, that's what it means," said Mr Lammy.
"There are no lateral flow testing going on in our prisons, which means that people can walk in off the street into our prisons, carrying the disease. This is very, very dangerous, and very, very worrying."
He added: "If our prison officers and probation staff are off work sick, who is running our prisons? Do we really want prisoners running our prisons? That's what we could be up against. So, we have to get a grip of this emergency now taking place across the country."
A Prison Service spokesperson said: "Mass testing, shielding and reduced contact mean infections are significantly lower than predicted at the start of the pandemic."
4,800 prisoners have contracted COVID-19 and at least 71 inmates have died since the start of the pandemic.
According to the Ministry of Justice, there were 2,400 positive cases recorded in December, a rise of nearly 70% in a single month.
Sky News understands there has been an outbreak of coronavirus at HMP Send in Surrey.
In a letter to inmates, the governor Carlene Dixon confirmed 22 prison staff and 6 inmates have tested positive after displaying symptoms.
As the first cases of COVID-19 began to spread inside HMP Coldingley in Surrey, ex-prisoner John Drake remembers how distressed he became when the facility was suddenly locked down.
"I didn't know if I was going to get out. I was worried about my family. I struggled to cope with how COVID turned the prison upside down. I really didn't think I would make it out," he said.
Mr Drake, 35, was released just over a week ago from the category C men's prison after serving a four-year sentence for robbery.
"I know a few people who were doing things to get out of their cells because they couldn't handle being locked up, with no one coming to you. It doesn't matter how many times you pressed that cell bell no one would come at all."
He claims offenders were kept in their cells for 23 hours a day and staff at times did not wear personal protective equipment when they could not maintain a two-metre space between prisoners.
"The staff never wore PPE," he said. "The only people who were wearing PPE were the nurses - the guards who would come around, they never had no masks or nothing."
He added the long months spent in solitary confinement have caused his mental health to suffer.
Around a third of prisoners have access to in-cell toilets at HMP Coldingley but four of the five prison blocks still do not have in-cell sanitation or washbasins.
At night prisoners are required to press a bell and wait in a queue to use the toilets and are allowed eight minutes to use it and return to their cell.
Mr Drake said due to limited hygiene facilities some inmates were forced to dispose of human waste in plastic bags and bottles.
He said the sanitary conditions left him and others at risk.
"We had no toilets in our cells, no sinks in ours cells, so we couldn't use the toilets. So, we have to urine in a bottle, or faeces in a carrier bag. Basically, it was inhumane for everyone. I think it's not right for any person to do that."
He added: "It knocks your dignity left, right, and centre. It's just wrong. No one should have to go through that. No one comes to let us use the toilet and with the sanitation system you could be waiting for hours to get out your cell to use the toilet."
The Ministry of Justice said every prisoner has access to their own hand sanitiser.
"These allegations are untrue. Prisoners have access to outdoor exercise and educational materials - while staff have adequate PPE and are trained in how and when to use it," a MOJ spokesman added.
For some vulnerable prisoners, being in jail amid a pandemic can be a "death sentence."
Richard, a former inmate released from HMP Bullingdon in Oxfordshire last month, said he was "terrified" he was going to die because of an underlying health condition.
"It was so bad," he said. "The staff didn't really know how to care for us. I have sickle cell disease which meant I would be at risk from coronavirus, but nobody shielded me or helped to keep me safe. We were all let out of cells all at once and forced to shower, let alone be socially distant from other people."
More than half of the 117 prisons across the nation have been impacted by the pandemic.
The head of the body representing prison governors said "to avoid further outbreaks" the government should consider putting prisoners and prison staff high on the list for vaccinations.
Andrea Albutt, president of the Prison Governors Association, said: "If more people die and we have more outbreaks, and we are releasing people worse than when they came in, then the solution is vaccinating."
"They have been locked down now in prisons since March. If we want to manage the risk effectively, if we want to make our prisons rehabilitate, to places again, and we want to get regimes up and running, so that when people come into our prisons, that we're able to make them better people, the way to do that would be to vaccinate."