In a London first, smokers in Beddington and Wallington are now forbidden from lighting up in public parks.
Sutton councillors have agreed the first outdoor smoking ban, which covers any public play area where children could be exposed to tobacco.
Other areas in the borough are expected to follow the example of the Beddington and Wallington local committee by voting to banish smokers from open-air spaces.
The council says a borough-wide ban would cost £20,000.
The decision was taken on Tuesday night after consultation showed 84 per cent of residents backed a trial scheme at Beddington Park.
But smokers’ rights groups have condemned the legally unenforceable ban, which relies on signs costing £3,200 to make smoking socially unacceptable.
The trial ban was imposed over the summer after Councillor Bruce Glithero complained that passive smoking left his daughter spluttering.
A spokesman for the Forest lobby group said: “Many politicians want to ban smoking in public but don’t have the courage of their convictions.
“Instead they are bringing in a ban through the backdoor in this sneaky and underhand way.
“The signs simply turn people against one another and are a pathetic and narrow minded attempt to bully people into quitting.”
Marion Williams, a Tory councillor for Beddington south, said: “Keeping children safe is a top priority but, rightly or wrongly, smoking in the open air is not illegal, therefore this ‘ban’ is useless.
“Alarmingly, Lib Dem councillors wanted to use police time on an unenforceable smoking ban, when we think they should be out catching criminals.”
The trial ban was imposed over the summer after Coun Bruce Glithero complained that passive smoking left his daughter spluttering.
Coun Jayne McCoy, the committee chairwoman, said: “I’m delighted local people have backed our efforts to protect children from smoking effects.
“This trial was put in place following concerns raised by residents.
“We always said the community would decide on whether to make it permanent.
“The strength of support shows local people are behind us, I hope the voluntary smoking ban is introduced in playgrounds borough-wide.”
Deputy council leader Ruth Dombey said stopping smokers lighting up outside, after 493 people returned consultation documents, was “an excellent display of local democracy in action”.
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