When Michael Portillo was at school, a close friend of his in the same class killed himself. They attended Harrow County School for Boys.

Explaining the reason behind making this programme, Michael says: "This film is an accolade to a very gifted friend who chose, almost 40 years ago, to give up on life. It is also a tribute to the courage of his parents who have suffered agony every day since."

Gary was popular, a gifted musician and a clever student, but just before his 16th birthday he committed suicide, leaving a note telling his parents he loved them and asking them: "Please, don't be sad".

In detailed and moving interviews with Gary's parents, Jeanette and Ronnie, and his younger brother, Andy, Michael learns how impossible it was for them to fulfil this plea. He discovers how Gary's suicide and his family's enduring sense of loss has coloured their lives ever since.

Gary's father says: "The terrible grief you feel immediately stays with you for the rest of your life. It was 40 years ago, and I'm 80 now and it's still exactly the same feeling."

The implicit message from Gary's family to anyone who may be in despair and thinking of ending their life is: "Please, think hard about the effect on those you are leaving behind."

This is inherently a sad film, but it is uplifted by the courage shown by the family in reviving such painful memories – through home video revealing a happy and carefree family, and by wonderful music, especially the music Gary himself composed, which was lost for 40 years. It was only rediscovered in the making of this programme and, here, is performed by his younger brother.

Michael Portillo – Death Of A School Friend is part of BBC Headroom, a two-year mental health and wellbeing project. It aims to raise awareness of the importance of good mental health and de-stigmatise the problems surrounding the mental illness issues which face up to one in four of the population, including anxiety, stress, depression and nervous breakdown.

Supporting the transmission is a mental health action line – 08000 933 193 – which offers callers advice about where to get support if they, or someone they know, is going through a nervous breakdown or dealing with other mental health issues. There is also a website, bbc.co.uk/headroom.