Police and bailiffs clashed with protesters in Rushcroft Road, Brixton as the eviction at one of the properties got underway.
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Council workers uncovered the AK-74 concealed in the undergrowth.
The thief, who used a walking stick, was helped by a man who disabled the lock before pushing the woman away.
More than 40,000 new property millionaires have been created across Britain this year so far amid rising house prices.