Diana's husband Adam told ITV London that the public need to stand up and say "this isn't good enough."
More top news
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.