Introduction 9Chapter 2Asteroids, Cometsand Near Earth Objects 11Chapter 3Environmental Effectson Earth 15Chapter 4Overall Risk 20Chapter 5Observational Techniques 22Chapter 6Current Activitiesand Future Plans 24Chapter 7Activities in Britain 27Chapter 8Mitigation possibilities 28Chapter 9What is to be done?including recommendations 30Annex AChronology 36Annex BImpacts and CloseApproaches of Asteroidsand Comets 39Annex CGround-based Telescopes...