The Highways Agency says it has filled the hole in the M2 in Kent with 40 tonnes of shingle.
This, officials say, has stabilised the hole and is helping them assess the extent of the problem.
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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.