for southend. police have arrested a man on suspicion of murder, and over the weekend they have been searching three properties in london. the man in custody is ali harbi ali, 25 years old and a british national of somali heritage. he went to school in croydon in south london. a few years ago he was referred to the prevent scheme, which is designed to stop people being drawn into terrorism. there are now calls to increase security for mps. the home secretary, priti patel, is considering police guards at constituency meetings. we must not let the terrorists alter our way of lives, but we also need to, as we move forward and push back against this, do this in a responsible way. for now, southend is in mourning for a man who dedicated his life to the service of his community. arun iyengar, bbc news. we're joined now by our political correspondent chris mason.