Conservative MP Amber Rudd said Margaret Thatcher would not be surprised that some people are using her death as an opportunity to protest.
Speaking to Daybreak she said: "Be very careful, because peaceful protests is ok, anything else is not."
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Dashcam footage captured the tree crashing down onto 40-year-old Sarah Robb's BMW just after she left her home in Syston on Thursday.
The teenagers, aged 19 to 15, appeared in custody at Westminster Magistrates' Court on Saturday, supported by their families.
Labour must "broaden its reach" in order to win votes off the Conservatives, deputy leader Tom Watson has said.