A citizens advice service, scout troop and mental health charity have each scooped £6,000 after winning a public vote.
They earned the cash in the Wimbledon round of the NatWest Community Force Competition – which asked charity supporters to back their favourite cause.
Debbie Chapman, a spokesman for winner Merton and Lambeth Citizens Advice Bureau, said: “We’re absolutely delighted.
"The money will be hugely useful to train some more advisers, who we desperately need. We’re over the moon."
She thanked Wimbledon Guardian readers for backing the cause and said a story featuring the charity's attempt to win the cash had prompted a spike in votes.
The organisation finished the competition, which began in September, with 218 votes.
Stem4, which is based in Wimbledon, won 245 votes.
It has promised to use the cash to deliver workshops on eating disorders in schools.
The 5th Morden Scout Group won 312 votes and will put its share of the prize towards a new minibus.
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