Guardian: The chances of a third runway being built at Heathrow airport have been dealt a serious blow after a government document warned that BAA cannot lodge a planning application for the project before the next general election. The Conservatives — who are well ahead of Labour in the polls — have pledged to block a new landing strip at the UK’s busiest international airport. The admission gives a Tory administration ample time to draft a new aviation policy that will block BAA’s …