Former Conservative cabinet minister Jonathan Aitken was convicted in 1999 of perjury and perverting the course of justice and served seven months in jail. Conrad Black, who once owned the Telegraph and has a seat in the House of Lords, was released from a US prison this year after serving time for fraud and obstruction of justice. This week they met to compare experiences. Susanna Rustin listened in.

Jonathan Aitken: Anyone who's been through the experience of incarceration as a high-profile prisoner faces special challenges. One way to succeed is to go with the flow and find a way of getting on with the guys you are in with.

Conrad Black: In the US system, 97% of prosecutions end in guilty pleas and 85% of cases that go to trial are convictions. There's huge resentment of such an over-mighty prosecution system and respect for anyone who fights it. Because mine was a famous case, and the prisoners saw my arrival on CNN, they thought here's somebody who fought the system. So I was sort of a good chap in advance.

JA: I pleaded guilty at the earliest opportunity. That's a much easier way to go through it. I found it harder coming out of prison than going in, because people's attitudes to you are so strange.

Susanna Rustin: How did you find getting out of jail?

CB: Extremely agreeable. Because I was not a US citizen, I was handed over to the immigration and customs enforcement agency and conducted to Miami airport where my wife [Barbara Amiel] was waiting for me. We had a charter and we went right to the front of the line and took off. It was a very happy trip. My wife normally takes a dim view of any form of drinking, particularly prior to noon, but she served me a very nice glass of white wine at about 10am.

SR: Do you remember your first night in prison?

JA: I do for one comic reason and one scary reason. The comic reason was that on the day I was sentenced I was the most notorious person in the country. When I got inside I was interviewed by a prison psychiatrist who was blissfully ignorant of who I was. When he asked, "Does anyone other than your next of kin know you're in prison?" and I said, "Maybe by now 20 million people know," he scribbled on his pad and became rather kind and asked had I ever suffered from delusions. The sinister reason was that when I got into my cell the prisoners set up a chant, and the gist of it was that Aitken has arrived, tomorrow morning let's show him! I now know that's what happens every night in Belmarsh. But I thought they meant it, so I was scared.

SR: Were you scared by prison?

CB: My spirits weren't lowered too much. My wife accused me of pretending it was Camp New Moon [a children's summer camp in Canada]. But I was worried about getting on. My background, like Jonathan's, is different from most of the people we were with and I didn't want to be an outcast. But they couldn't have been nicer, and I soon recognised the politics of the place – there were heads of ethnic groups and factions. The first night I was there, a mafioso came over and said nobody would bother me.

JA: Some people said to me, once you're out you'll go back to being a big cheese and forget about us. And I haven't. I made one tremendous friend in prison, and until he died recently I saw him twice a week. At my wedding [to Elizabeth Harris in 2003] by some strange statistical quirk there was the same number of ex-cabinet members as ex-cons.

SR: Did prison change your views on criminal justice?

CB: I was always rather liberal on these matters in American terms. We have to make a special case for violent people, obviously the public has to have some protection from them. But I think prison for non-violent people is nonsense.

SR: What is the appropriate punishment for people convicted, as you were, of financial crimes?

CB: Working for free, or if they have no means of support, then living in shelters [hostels] under a basic regime, contributing their service to designated causes. If you get recidivism you have to imprison people, but most in my opinion would not be repeat offenders.

JA: I get called a prison reformer now, and in a sense that's true, but the reforms this country ought to focus on are not the prison system, which is quite decently run, but rehabilitation.

CB: In the US private prisons are always agitating for more criminal offences, longer sentences and a larger prison population. It's just like any other business, only more tawdry and corrupt.

SR: What does it feel like to fall from the pinnacle of the British establishment to public humiliation?

CB: I was so contemptuous of the process by which I was sent to prison that I was determined not to let it diminish me. It was a novelty. I had never been in a milieu like this before, so I was naturally curious. I was relieved it wasn't more difficult. It was tedious and it was unjust that I was there at all. But I didn't find it humiliating.

JA: The struggle is to survive and say, I'm going to start again, I know I've got to have a different life but it may not be a worse life. I don't want to minimise the struggle of it, but I think reasonably strong characters – and I suspect Conrad and I could both be put in that bracket – are not going to go to pieces. The question is, how do you come back from that?

CB: I got messages of support every day and found them very encouraging. Some people I took to be friends were disappointing, but many people from whom I had no right to expect anything filled up much of that gap. I thought Rupert Murdoch [whose newspapers criticised Black] revealed himself as an absolutely beastly and terrible man, despite his very great achievements.

JA: I start from the notion that the "hoops of steel" club, as Shakespeare calls it, is very small. My friends in that category were rock solid. There were surprises among the rest. Two days after I was released, Denis Thatcher asked me to lunch at his club. I think if I was to go through the disappointments list with Conrad, we might find some people in common – Max Hastings for example.

SR: How important was religion?

CB: If you believe in God I think it's much easier to believe there is some purpose even when inexplicably unjust things are happening. Also, there's the idea that a setback on this scale is something you must draw a lesson from and work hard to see what the lesson might be. History is full of people who did come back from terrible setbacks and so you never lose hope. You aren't out of the game altogether, you just have to regroup.

JA: I would hate to have gone through all this without there being a huge spiritual element. To this day I do quite a lot of faith-based work in prisons.

SR: Should prisoners have the vote?

JA: No for constitutional reasons. I hate the idea of the British being pushed around by Strasbourg judges.

CB: For me there is a distinction between people convicted of violent crimes, who I think while they're in prison shouldn't have the vote. And the others shouldn't be in prison anyway so they should.

SR: Jonathan's first marriage ended in divorce. Did your marriage suffer?

CB: I think it was more difficult for my wife because she had a lonelier life without me. She doesn't like Florida, but she stayed there a lot because it was near to me. In the summer it's terribly hot and she has these magnificent dogs that have heavy fur coats. It was very uncomfortable for them.

• A Matter of Principle by Conrad Black is published by Biteback, price £14.99.