Mayor Boris Johnson has promised to look again at Crossrail construction safety after a worker was electrocuted.
During the Olympic construction, a collective agreement on health and safety was put in place between the construction firms and the unions. The mayor was asked whether a similar agreement should be introduced for Crossrail.
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David Cameron said the Met proved it can "do more with less" and declined to criticise the Mayor of London for his water cannon spend.
A group of disabled activists threw toys and balls at him as he entered the conference.
A wet start to the week and the unsettled weather is set to continue over the next few days.