It was the evening of December 21, 2000 when I discovered my brother Bill’s secret. The circumstances were harrowing: customs officials crashing into my house armed with a search warrant. But even before they arrived, I was in a state of shock. Three weeks earlier I had discovered Bill’s body sprawled on the floor of his West London flat.

Bill was my adored older brother. He was also a brilliant journalist (he was chief reporter at The Times). He and I were always close, and told each other more than our partners sometimes felt comfortable with. I was the first person he rang each morning and, after the break-up of his marriage, the last person he spoke to at night. I thought I knew everything about him.

Ten days earlier I had stood paralysed by grief at his funeral. The death certificate said he had died from a pulmonary embolism – a blood clot that travelled from his lung to his heart – and registered his death as due to natural causes. But the harrowing breakdown of his body and mind from alcoholism and Class A drugs had taken several years. During that time I had battled with Bill in my attempts to try to save his life. I had coaxed, pleaded and, when all else failed, sometimes just sat and wept helplessly.

Losing him was always my greatest fear. Now, just as I thought that life could get no worse, two customs officers had handed me a warrant. I read the words incredulously: “There are reasonable grounds for suspecting that Kevin Stephen Patrick Hanley and William Robert Frost have carried on, or have benefited from, drug trafficking”.

Yes, Bill was a cocaine addict. But he was a victim, not a perpetrator, of drug crime. Kevin Hanley was the younger brother of Bill’s last girlfriend. From 1994 onwards he had been a frequent visitor to Bill’s house, sometimes staying there when Bill was at work. Once or twice Bill had told me not to worry if I noticed that the blinds were down – Kevin was trying to avoid someone who was looking for him. I assumed that he was involved in an extramarital affair.

I was shocked when Kevin was arrested in 1998 with a car boot full of cocaine – 29 kilos of it. After that Bill’s behaviour went off the dial. He was drinking and increasing his use of drugs, including crack, as if on a mission to self-destruct.

Sometimes he would clutch at my hand as we parted as if about to confide something. But when I prompted him he would shake his head and turn away, muttering “safer not”. Visiting him in a flat in Notting Hill one day I was horrified by his appearance. Although then just 48 years old, he looked like a gaunt old man, physically shaking and psychologically paranoid.

But of one thing I was always certain – that my brother would never have been involved in anything that traded on human misery. When we were children, he had been my protector and defender. Bill was a born risk-taker, a fearless war reporter. But he was also a kind, moral and compassionate man with a strong sense of his own survival. Addiction might have made him a fool, but he was no villain.

That visit by Customs started me on a search to find out more about my brother’s secret life. Over the course of the next five years I found out that Bill had indeed been involved, if only on the margins, in the international cocaine-smuggling operation of which Kevin Hanley was the “lieutenant”. It appeared that Bill had leased property for the man he called his “brother-in-law”, as well as paying the lease on a caravan in Hampshire where the conspirators had stayed.

All I kept thinking was: “Why didn’t you tell me, Bill?” I started to wonder how well we ever know those closest to us.

Even more surprising to me was the discovery that Bill had sometimes spent up to £500 a day at the bookmakers. I had never known Bill to put £2 on the Grand National. The more I found out about the last five years of Bill’s life, the less I felt I knew him. I looked for reasons for his self-destruction but never questioned my feelings about him. Ultimately he had become so weak that his dependency had claimed his life. I do not think any the less of him for that.

I remember my mother telling Bill and me when we were small that when you loved someone it didn’t matter what they did. You still went on loving them anyway. Seven years on from Bill’s death, there is still much that I don’t know, and certainly don’t understand, about what he did and why. But I still love him as intensely as ever. I just wish I had known.

Out of It: How cocaine killed my brother, by Clare Campbell, is published by Hodder and Stoughton, £15.99

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