Policing powers for park staff to try to stamp out antisocial behaviour have been criticised by experts.
They spoke after rangers in St Albans, Hertfordshire, and wardens in Southwark, south London, were given powers to confiscate alcohol and punish litterbugs and cyclists on footpaths.
Grounds-upkeep firm John O'Conner said rangers in St Albans had instant radio links with police, but experts said "have-a-go heroism" had no place in parks.
Under a Community Safety Accreditation Scheme, launched in June 2010, four staff could ask for names and addresses of antisocial park users. Now they can seize alcohol from suspected underage drinkers in the three main parks.
Managing director Matt O'Conner said: "This is not intended as a police substitute but an extra set of eyes and ears. Our role is not confrontational and the police have said that if a situation looks like turning nasty we should back off and inform them."
Meanwhile, Southwark and the Metropolitan Police have given 49 wardens powers to fine in Burgess, Dulwich and Southwark Parks and Peckham Rye. Offences include cycling on footpaths, begging, fly-posting, dog fouling, littering and selling alcohol to children.
A Southwark spokesman said: "They don't have powers of arrest but if people refuse to give their details it becomes an offence and the police can then get involved."
Parks consultant David Lambert said: "Rangers aren't paid to take this kind of risk. Unless they receive the training police get, it shouldn't even be contemplated. This sounds a reckless and unreasonable demand."
Consultant Sid Sullivan said: "Turning parks staff into pseudo police will be costly, while parks continue to deteriorate. It will also bring staff into somewhat violent contact with the public."
49 - Number of wardens granted the power to fine in Southwark