The UK’s leading maker of methadone, which is used to treat heroin addicts, has been put up for sale by Cardinal Health, its US parent, attracting interest from a crowd of private equity groups.

Martindale Pharmaceuticals, which controls about half the methadone market in the UK, also makes diamorphine, a legally prescribed controlled form of heroin, as well as more than 100 generic drugs, including adrenaline, morphine sulphate and codeine.