Prewett's biscuits Full Coated Bourbons 165g. Delicious gluten free chocolate flavour biscuits with a chocolate flavour filling coated in milk chocolate.. Since 1872, when William Prewett began miling flour in Horsham, Sussex, the Prewett's name has been synonymous with fantastic free from quality biscuits. Prewett's biscuits are simply delicious & amazingly, they're Gluten free & wheat free.