What is it really like to be a teacher in a prison? Are you simply just a part of the "soft" side of things - a do-gooder in the tradition of the well-intentioned but naive Mr Barraclough from the classic prison sitcom Porridge. Or are you risking life and limb every time you turn up for work, putting yourself into a dangerously explosive environment over which you have little control?
Cue those images from back in 1999, when Britain's most notorious prisoner, Charles Bronson, went on the rampage at Hull Prison. The hostage he took up on to the roof with him was a teacher- prison educator Phil Danielson.
Bronson tied a leather skipping rope around his neck and for two days proceeded to lead his hapless captive around like a dog on a leash.
In order to answer such questions, I find myself, one autumnal morning, going behind the wire-topped walls of Highdown Prison on the southern outskirts of London.
Built to accommodate the growing prison population of the 1980s, Highdown is a Category B local prison with around 750 inmates. It is not a pretty building - sickly pale breeze block predominates - but it is light and uncluttered and a world away from those 19th-century institutions that most of us associate with the word "prison".
I am met by the aptly named Evelyn Nickford, who runs the education service inside Highdown. Evelyn cheerfully admits to being "hooked" on prison education and talks of her own 14-year "stretch", which began back in 1990 and continues today with little prospect of early release.
It is clear as we progress through her domain - a purpose-built mini-college with nine classrooms and specialist rooms for cookery, hairdressing and art - that Evelyn is an unashamed prison-ed enthusiast.
"There's a real buzz about teaching in a prison that you just don't get outside," she says.
The atmosphere inside is not at all oppressive, although every doorway we go through must first be unlocked - one steel door plus a clunky metal grill that piggy-backs on to it - and then locked again behind us.
We go into a classroom. Inside, half a dozen men are sitting around a large table, working individually on improving their literacy. There is a relaxed atmosphere and the teacher, a woman in her forties, passes from student to student, helping and encouraging them in their work.
I talk, rather awkwardly at first, to several of them. Coming in from the outside - "We've got a visitor today" - you feel a bit like the Duke of Edinburgh parachuted in to open something: "What is it that you do?" "I'm a prisoner mate, and yourself?"
But once the ice has been broken, what comes through again and again is the pleasure that these men are getting from their education.
Jimmy is a case in point. He has problems at times in getting his words out, but he is still able to tell me candidly that he did not go to school much after the age of 14. "Well, to be honest pal, it was more like 12. But now..." - he points to a certificate on the desk beside him - "I've got that." It's issued by AQA and states for all who care to see that Jimmy is now the holder of an entry-level qualification in literacy. "It's the first thing I've ever passed in my life," he says with such pride you almost want to hug him.
Evelyn's big bunch of keys come out again and we go into another teaching room. This time it is numeracy. Basic skills are what the vast majority of prison education is about now. These are not master criminals but rather life's perennial underachievers who just happened to get caught.
Once again, as in the literacy class, there is that pride - joy almost - in what they are achieving. Delroy shows me his exercise book full of sums, turning page after page, pointing proudly to the profusion of ticks. "I learned nothing at school, man, nothing."
That contrast - between what it was like for them in school and what they are experiencing now - comes up all the time. "When they realise that we're not the school teachers they failed with, there's this massive sense of relief," says Helen Holmes, Highdown's acting basics skills co-ordinator.
Like Evelyn and like the men, Helen unashamedly bangs the drum for prison learning. "First impressions are vital. When I go in, I say, 'Forget about being in a prison, you're in class now. What's your first name?'"
The first name thing is important too, as is the fact that none of the tutors wear uniforms. "It gives them a sense of being an individual which contrasts with the regimentation of a lot of the rest of their life in here," adds Helen.
So, have I found the answer to my question as to what it is really like to teach behind bars? Those initial stereotypes have certainly taken a bashing. Take the issue of danger, for instance. Helen, a slight woman in her early thirties, laughs at the idea that she may be under threat. "I don't feel threatened by my students, because I know them."
The sentiment is echoed by the other tutors - all women - I speak to. One says, "To be honest I feel safer in here than I do teaching outside. I've got a personal alarm which would bring half a dozen hefty officers to my aid if I needed them. And anyway, if someone causes trouble, the other men would help me."
And what about that "do-gooders" label? Well, yes, they do "do good". Like teachers anywhere they get their job satisfaction from the achievement of their students. "Even the little things mean a lot in here," says preparation for work tutor Liz Trumper. "Just an apology from a student can give you a lift."
As I prepare to leave I joke with the tutors that the one thing they don't have to contend with is student lateness. "It happens all the time," they chorus. One adds: "Something happens on a wing and they don't turn up till half your class is gone. And then, if you're inspected, you get the blame for it."
Now that really is like teaching on the outside.