Bonnets are back on Sunday evenings on the box. After Mrs Gaskell's Cranford, here comes Charles Dickens's Little Dorrit. It's a book made resplendent by the unforgettable depiction of the Marshalsea debtors' prison. It's where at the start Amy Dorrit is born to the hopeless bankrupt fantasist William Dorrit who is still vegetating in the prison when the narrative proper gets going 20 years on.

It's Amy who tugs the heart-strings as she looks after useless father, brother, uncle and sister, cheerfully and loyally. Into their lives comes Arthur Clennam who is returning to London after years in China. He finds Amy working for his mother, a woman not given to charity and he's intrigued to know why.

Hull's Sir Tom Courtenay, who rarely does TV these days, portrays William Dorrit. "The adaptor Andrew Davies and I are very old friends, we were at university together," says Sir Tom. "We worked together very happily on A Rather English Marriage a few years ago, and it's lovely to be collaborating with him again. His scripts are brilliant. This has been a very happy reunion." The other element that drew Courtenay to this was his deep and longstanding love of Dickens. "I know my Dickens pretty well. Alongside Shakespeare, he has been my favourite writer since I was at school. I used to love reading his books aloud.

"People adore Dickens because of his stunning imagination. Actors love him because of the huge number of marvellously rich characters he creates. Quite simply, he was a genius.

"William Dorrit has been living in prison so long he has got used to it. When he finally gets out, life is not as he's imagined it would be and he realises that he is actually happier in prison. He's a less well known part than, say, Mr Micawber, but in fact he's a much richer character. He goes through so many ups and downs and in so many different directions, sometimes simultaneously. That has made him the most terrific fun to play. The main aspect for me has been William's relationship with his daughter. She is wonderful to him and helps him get through it.

"I've always wanted to be in a TV adaptation of one of Dickens's novels. So now this is my opportunity, and I'm loving it!"

This is a book where a vivid selection of London life walks off the pages. It's an extraordinary and compelling collection of landlords and rent collectors, plasterers, bankers, turnkeys, prisoners, gentlemen and paupers, wastrels and dancing girls, engineers, artists, dowagers and butlers.

The ungainly plot is explained by the fact that is was originally a monthly serial published over 19 instalments with cliff-hanger endings.

This adaptation is in keeping with that style. It's broadcast in half-hour "soap-sized" episodes – an idea that worked a treat for the award-winning Bleak House which was also the work of Andrew Davies, who says: "It lends itself very well to this format – Dickens has the robustness of story and character to sustain half-hour episodes.

"You can cram an incredible number of people and incidents into a half-hour without viewers feeling they're just being given snippets."