Keith Hellawell, Chief Constable of West Yorkshire, and Raymond Kendall, secretary-general of Interpol, both said they backed decriminalisation.
Mr Hellawell - who has called before for soft drugs to be decriminalised but not legalised - said this position was now the policy of the Association of Chief Police Oficers.
He told the association's national drugs conference in Wakefield, West Yorkshire, that drug use in large areas of Britain has been in effect decriminalised. More than half of the first-time offenders who took soft drugs, mainly cannabis, escaped prosecution and were cautioned.
Mr Kendall, a former Scotland Yard detective, said: 'If someone is caught with drugs they should be treated, not convicted. The difference between hard and soft drugs is a smokescreen - I don't see any difference between them.'
Mr Hellawell said British police forces could not support such an approach and legalisation of drugs was 'not on the agenda'. He is currently studying the effects of the greater use of cautioning and is due to report back to the association later this year.
Mr Kendall told BBC Radio 4's World at One programme that he supported the decriminalisation of all drug use.
'I am in favour of decriminalisation but not in favour of legalisation,' he said. 'I think we should accept the reality of the situation . . . that there are many, many drug users who are living in a situation of illegality already.
'Since they cannot be brought into the justice system and the police are simply cautioning generally the average cannabis user, we have a situation that says most of these people are not being dealt with by the law, which is not a healthy situation.'
These views were countered by John Major, who said during a visit to Cleveland that he was completely opposed to the decriminalisation of soft drugs. 'I don't believe that is right,' he said.
'I understand why some people approach the problem from that angle but I profoundly disagree with it. I fear that if you make it acceptable for people to have drugs, they will find it acceptable and they will move from soft drugs to hard drugs, so I don't at all personally favour decriminalisation.'
Lord Mancroft, a Conservative peer and drugs campaigner, who addressed the Acpo conference, said drugs should be sold on the high street in narcotics 'off- licences'. Lord Mancroft, a member of the All-Party Misuse of Drugs Group, called for the legalisation of drugs to combat the growing black market.
He said: 'The black market in drugs is fuelled by money, so the first step must be to remove the profit.
'By supplying drugs to those who really want them through government-controlled outlets, a sort of cross between an off-licence and a chemist, at a realistic price, the need to purchase from the black market is eliminated.'
He added: 'The great majority of cannabis users encounter negligible problems . . . Using the criminal law as a means to prohibit the use of drugs has failed.'
The Home Secretary, Michael Howard, will address the conference today and reaffirm the Government's opposition to decriminalisation. He will emphasise its commitment to tackling the problem at source by curbing supply and demand.Reuse content