Britain's two busiest airports have closed as a volcanic ash cloud drifts further south, threatening major disruption to many thousands of people. A no-fly zone imposed by the Civil Aviation Authority ceased Heathrow, Gatwick and London City airports. Flights are also grounded in parts of Scotland and Northern Ireland. Manchester, Liverpool and Leeds Bradford airports have re-opened after restrictions in the north were lifted. Birmingham, Norwich and East Midlands airports are also open again, after suspending flights yesterday.