BRIGHTON, England (Reuters) - London Mayor Sadiq Khan said police had thwarted seven attacks by militants since March this year, describing the increase in the number as a shift rather than a spike. Speaking at the annual conference of his opposition Labour Party, Khan also said the police needed more spending to help them counter such attacks and that Internet companies must do more to crackdown on extremist content.  Between March this year and now, there have been four attacks but seven have been thwarted,  he told a Guardian Live event. Earlier this month, the head of the city s police force said six militant plots had been foiled over the last several months.     