A house fire that killed a mother and her five children in Harlow, Essex, last month is now being treated as a murder investigation, Essex Police said tonight.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.