Britain said on Wednesday it had leased a barge to house 500 migrants on its southern coast as part of efforts to reduce the use of costly hotels as temporary accommodation while asylum claims are being processed.Prime Minister Rishi Sunak has made cracking down on illegal migration one of his top priorities ahead of an election expected next year and has set out plans to bar the entry of asylum seekers arriving in small boats across the Channel.The vessel, the Bibby Stockholm, will be berthed in Portland Port in Dorset and will accommodate 500 single adult males, Britain's interior ministry said.Migrants will be moved aboard "in the coming months" and it will be operational for at least 18 months…