The Office of Fair Trading Distance Selling Regulations place the responsibility for items lost in the post squarely with the seller. Please see their guidance notes (especially sections 3.36 and 3.20) for further details. This document contains clear information on a range of issues that buyers and sellers may face. The guidance can be downloaded from
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follow the top link and choose the option to "Download our business guide Home Shopping: Distance Selling Regulations (pdf 127 kb).'