Arsenal manager Arsene Wenger has told a press conference that he believes ball boys should be educated, and that their job is simply to get the ball back into play as quickly as possible.
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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.