By chrisdorney / GEtty Images The cliff-top ruins of an ancient castle long claimed as the birthplace of the legendary King Arthur is “at risk of being lost for ever” as climate change quickens the pace of coastal erosion, a UK heritage body warned on Friday. The cliff-top ruins of an ancient castle long claimed as the birthplace of the legendary King Arthur is “at risk of being lost for ever” as climate change quickens the pace of coastal erosion, a UK heritage body warned on Friday. Tintagel Castle in Cornwall, southwest England, attracts tens of thousands of visitors each year, fuelled by t…