GEMMA Jones is one of Britain's most highly thought of actresses.

She is best known for her roles as Bridget's mother in Bridget Jones's Diary, and Bridget Jones: the Edge of Reason; Madam Poppy Pomfrey, the matron of the hospital wing of Hogwarts School in three Harry Potter movies and as Mrs Dashwood, mother to Emma Thompson and Kate Winslet, in Ang Lee's Academy Award-winning period drama Sense and Sensibility.

Gemma also plays a major role in Tom Browne's Radiator, a profound study of how time changes parents into children and children into parents, that features in the four-day Keswick Film Festival, opening next Thursday, February 26.

Filmed in Mungrisdale in the actual cottage in which director and actor Tom was brought up, Gemma plays Tom's mother alongside another distinguished film and TV actor Richard Johnson, as his father.

"Radiator is a lovely film and I'm very proud of it," explains Gemma.

"It was a most unusual and rather extraordinary assignment. Initially it was the script that I loved, before I knew how autobiographical it was, and before I knew we were to be filming in his parents home. It was just a very lovely script. So that grabbed me first off. And everything else was a wonderful bonus. Obviously Tom was very close to the story and we had a very sensitive director.

"Everyone really got on well. Richard Johnson I had worked with before. Nothing felt too scary, we all knew each other. Because it was quite brave, what we were required to do. Particularly Richard. He’s an elderly man but he has incredible energy and stamina. He acted brilliantly.

"I never wanted to see a photograph of Tom's mother, because I wanted to play the person in the script rather than trying to imitate someone. But that never seemed to be a problem for Tom, he never said anything to me like "My mother would have..." So I got a great sense of her, and it wasn't until we'd finished that I actually saw a photograph of her. I must have had a sensibility that wasn't entirely different to Tom's mother's, something that I could express.

"I was sort of playing my own age span, which was nice. I wasn't particularly flattered in my role as far as the look, but I quite like that, I enjoy playing raw and real. I think Richard's and my intention was always not to be affected in any way, just to play the scenes as written and be as true to the moment as possible.

"I would like to think that the film is a nice memorial to Tom's parents, but without being at all mawkish or sentimental. It's quite raw at parts, and that's honest. I think they would have appreciated the honesty. "

Gemma's own father actor Griffith Jones, lived to be 97 but passed away eight years ago. He kept working until he was 90 with the Royal Shakespeare Company.

Gemma (born Jennifer in 1942) trained at RADA where she won the Gold Medal in 1962. Shortly after graduating, she appeared in The Cavern, for which she won a Clarence Derwent Award for best supporting actress of the year.

She toured the world in the early 1970s with Peter Brook's famed production of A Midsummer Night's Dream and appeared in the US with the National Theatre's 1994 production of The Winter's Tale. She is fondly remembered in the UK for her starring role as the lower-class cook turned upper-crust hotelier in the BBC's The Duchess of Duke Street, for which she won her third BAFTA nomination.

Gemma is an avid walker and while filming Radiator had time to stretch her legs.

"I am a hill walker, so, I had some good stride outs on my day off. I was first introduced to the Lake District when I was about 10 or 11 and we had a family holiday in the spring and stayed in Borrowdale. I remember it distinctly, it was a wonderful holiday full of long walks. My father would drag us, me and my mother, out for walks and then we'd come back for huge high teas. It is a very beautiful part of the world. My family home is in Wales, so when I have time off I go there. Which means I haven't been to the Lake District as often as I'd like really. It's extraordinary when you see how small it is on a map, but when you get up on the hills you could be miles and miles from anywhere."

Star of stage and screen, her acclaimed television work also includes Jane Eyre, The Borrowers, the BAFTA-award winning Longitude, Trial and Retribution, and as Dr Jakes alongside Harry Potter co-stars Emma Watson and Richard Griffiths in Ballet Shoes (2007).

Her big screen debut was in 1971 in Ken Russell's The Devils.

"Maybe I was very naive, but I didn't realise it was going to cause such controversy," adds Gemma.

"It was an enjoyable shoot, but I was playing quite a chaste character, I was Oliver Reed's wife, and I didn't have to do anything too alarming. I was a sort of innocent. It had the most amazing sets that were build by the painter Derek Jarman. He designed these sets which were huge in scale and geometric and most unusual at the time. It seems pretty tame now, but I suppose at the time it was a bit wild. We all wanted to do our best for Ken Russell, who created a great atmosphere on the set of wanting to do what he wanted. It was only in retrospect that we all turned around and said, well, maybe we were a bit abused. It's been recently remastered, there's a new version which I think you can get. It's worth seeing.

As for Harry Potter, Gemma said she hadn't read any of the books before she was asked to play Madam Pomfrey: "But I was very happy to be offered the role. It's not a big role, but I get so much fan mail from children now, which is rather wonderful. What is thrilling is that they were engaged by the books first, as well as by the films. I was proud to be part of it. Because all of the children acting in the film had to be educated, our days were sometimes very long. There was a lot of sitting around in each other's caravans and having a jolly good time gossiping in-between set-ups. It was like a big club, because so many of us knew each other. That was very enjoyable."

And Bridget Jones, I ask?: "That was great fun.

"There has been talk of a third film but they haven't been in touch yet. Jim Broadbent and I talk sometimes and he said if they were thinking of doing another one they had better hurry up or we'll both be on zimmer frames."

Radiator is screened on Friday, February 27 at 3pm at Theatre by the Lake.

Keswick Film Festival box office 017687-74411 or visit www.theatrebythelake.com.