 Warren was regarded as an energetic strike leader.As well as his work setting up pickets and speaking at union rallies and conferences, he demanded a minimum wage (of £1 an hour) and campaigned to put an end to "the lump" — a practice prevalent on non-unionised building sites, whereby the employee surrendered their employment rights in return for a cash lump sum with no tax or insurance deducted.His death in 2004 from Parkinson's Disease has been linked with the long-term effects of the treatment he received during his incarceration, in particular the "liquid cosh" – a cocktail of tranquilisers administered to inmates.