Tory leadership candidate David Davis has promised to deal “ruthlessly” with under-performing schools if he becomes Prime Minister, shutting down those that fail their pupils. He called for an “excuse-free zone” in education, warning that reform of the school system had stalled and the weakest pupils were suffering most from falling standards. Mr Davis, considered an outsider in the contest, set out detailed proposals on what is expected to be a key issue in the leadership battle during a visit to Archbishop Tenison’s school in south London, named last year as one of the 29 most improved in the country.