Nearly four million viewers are tuning in to watch her play a woman living with dementia in ITV’s Unforgotten. Here, actress Gemma Jones reveals why she decided to take on such a gruelling role.

With a star-studded cast including Sir Tom Courtenay, Trevor Eve and Nicola Walker, six-part drama Unforgotten, has millions of viewers gripped by its dark investigation of an historic murder.

Whilst unravelling the lives and secrets of potential suspects, detectives call upon wheelchair bound Eric Slater (Tom Courtenay, Dr Zhivago) who is under suspicion for the murder and his wife Clare (Gemma Jones, Bridget Jones’ Diary) who has dementia. Her portrayal of a confused but still insightful woman in the grips of early- to mid-stage dementia is unnervingly realistic, so it may come as no surprise to discover that Gemma Jones has personal experience of Alzheimer’s, the most common form of dementia.

‘My mother had Alzheimer’s and it’s a desperately cruel thing to witness,’ the Bafta-winning actress said recently, admitting she was initially resistant to playing the role because of her personal experience.

‘But then I thought, “I’ll do it for my mum” and so that was very challenging.’

Unforgotten also stars  Sanjeev Bhaskar & Nicola Walker as police detectives Unforgotten also stars Sanjeev Bhaskar & Nicola Walker as police detectives

Playing her husband and carer was also a learning experience for the distinguished British actor Sir Tom Courtenay, 78.

‘Claire’s dementia is challenging for Eric and his sons and it’s a fact of everyday life for many families,’ he says. ‘We all get forgetful, naturally, as you get older. You walk into a room and you can’t remember why you’ve gone in there. But I’m told that is a very natural and normal thing - it’s not the same as dementia.’

Gemma, 72, is now pleased she took on a role which was initially so difficult.

‘I’m glad I did it,’ she adds, ‘although it was very painful.’

Episode 5 of Unforgotten will be screened on Thursday at 9pm. To catch up on previous episodes, click here.