Alastair Campbell has opened up about the moment he reached crisis point in a London park while walking with his partner – journalist Fiona Millar. 

The former Downing Street press secretary has lived with depression for most of his life, and has been taking antidepressants on and off for 30 years. In a new documentary which airs tonight on BBC Two, and forms a three-part series on mental health, Campbell reveals exactly what depression feels like to him.

“It has a colour, a texture, it has a feel,” he explains. “It’s like a really unpleasant jelly type thing. And then it just sort of comes over and…” – he makes a gesture as if it’s coming down over his head, enveloping him. “It’s not that I personify it, but I can visualise it.”

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It’s thought one in six people will experience depression in their lifetime. Symptoms are unique to each individual and can range from mild to severe – from being persistently low in spirit to feeling as if life is no longer worth living.

The documentary sees Campbell try out different therapies in a pursuit for a cure, or at least a better way to treat his depression.

Discussing medication, which he has taken for years, he admits: “None of them can stop it.” He has tried several types of antidepressant throughout his life, experiencing side effects such as tiredness, lethargy and a sense of numbness. He has been on one type for the past three years which he says has helped keep him relatively buoyant.

He notes that they aren’t a cure but he needs them to survive.

Campbell, a former journalist, also talks about the at-home therapies which help to keep him from spiralling downwards – such as work, music, keeping fit: “If I don’t keep physically active, I risk a plunge.”

[Read more: David Harewood retraces his psychotic breakdown in emotional documentary Psychosis and Me]

At one point in the show, he sits down with his partner Millar to discuss the day he reached crisis point on a walk in the park. He became so angry and upset that he started punching himself in the head.

He recalls: “The reason I got so angry and frustrated that day, was actually I was thinking: ‘This fucking depression is never going to go, it doesn’t matter what I do it’s never going to go. It’s quite a hard thing to deal with’.”

Throughout filming the series, he kept video diaries to chart his mood. He has to rate each day from one to 10 – one being happy, 10 being suicidal.

The show opens with him discussing how he went from happy to suicidal in the space of minutes at the dinner table. “There’s no logic to depression. Having a loving family and a comfortable life has never stopped mine,” he says.

Campbell’s late brother lived with schizophrenia and the documentary also sees him open up about the time he thought he too was developing it.

He couldn’t think properly and felt like he wasn’t there. He started emptying his pockets and bag onto the floor. In the end he was detained by police.

He recalls hearing voices, bagpipes and brass bands, and television shows playing in his head. Afterwards he found out he was in the grips of a psychotic breakdown – although he hasn’t experienced one since.

Campbell describes the experience as “a cacophony of noise inside my head”.

Useful websites and helplines:

• Mind, open Monday to Friday, 9am-6pm on 0300 123 3393
• Samaritans offers a listening service which is open 24 hours a day, on 116 123 (UK and ROI – this number is FREE to call and will not appear on your phone bill.)
• The Mix is a free support service for people under 25. Call 0808 808 4994 or email: help@themix.org.uk
• Rethink Mental Illness offers practical help through its advice line which can be reached on 0300 5000 927 (open Monday to Friday 10am-4pm). More info can be found on www.rethink.org.