There are 14 privately run prisons in England and Wales and on Friday I received an email informing me that I am banned from visiting two of them, not by G4S who had invited me, but by the Ministry of Justice.

My charity, the Howard League for Penal Reform, argues that making money out of punishing people is both reprehensible and immoral and it is on these grounds that we have opposed the private management of prisons. Successive governments have privatised prisons, so it is not a party political issue. It has been claimed that introducing private sector competition into the penal estate has driven up standards but there is no evidence for this, indeed suicide and violence rates, along with similar evidence, points to the contrary. The only rigorous research commissioned by the Ministry of Justice to compare the two systems has never been published; I am told that it does not support this contention.

The letter sent to Frances Crook. Photograph: Twitter

I have seen good and bad practice in both private and public sector prisons, having spent 25 years working in the system. I have never been a fan of G4S, indeed we have been pressing the Serious Fraud Office to pursue its investigation into the various companies accused of fraud on the tagging contract more vigorously. However, I accepted the invitation to visit two of the G4S prisons to see for myself. Private prisons are taking £500m of taxpayers’ money each year, so they have to have independent scrutiny.

I was due to visit Oakwood, one of the biggest prisons in the country, which had a very rocky start, with allegations that it was easier to get drugs than soap. I was also due to visit Birmingham, the first Victorian prison to be taken over by a private company. I wanted to see what improvements had been made in both jails.

I understand that the company informed the Ministry of Justice several weeks ago that I had been invited and it is bemused as to why it took so long to inform me that my visit was being prohibited. The implication is that the decision was taken on high.

The most surprising aspect was the crude letter sent to me by a senior civil servant. Had the MoJ wanted to stop me visiting, it would have been simple to write a carefully crafted letter suggesting that operational reasons, or sensitivity due to the election meant that at this time my visit was inappropriate. I would never have permitted a letter like this to be sent by one of my staff, and it is an indication of an atmosphere created at the very top.

When I posted the letter, without comment, on Twitter, it went viral because it was so rude. It was retweeted, favourited, linked and commented on in social media tens of thousands of times.

It is all the more amazing because today Lord Woolf has said that prisons are in as bad a state as 25 years ago when he investigated the cause of the riots in Strangeways and 20 other prisons. The triple whammy inflicted on prisons by government policies means that they are dangerous, violent places. They closed 18 prisons and relocated tens of thousands of men to the remaining jails. They cut staff numbers by more than a third. They allowed the numbers of people going to prisons on remand and under sentence to rise.

Report after report by the chief inspector of prisons and by independent monitors have told how people are locked in their cells with nothing to do for weeks on end and that violence is rising. If we treat people like this we cannot expect them to emerge into the community magically transformed into law-abiding citizens.

I recently spent time with the family of an 18-year-old young man who had only spent a day in prison when he hanged himself in his cell. He was one of 82 people who took their own lives in prisons last year. Things are going badly wrong and we have to tell it like it is.