Giles Fraser's 'Thought for the Day' has figured here before. Today he mentioned the demise of the old one-pound coin and its inclusion of the motto 'fid. def.', which he said was an abbreviation of 'fides defensor'. It isn't: it should be the genitive form, 'fidei defensor'. Quoting Latin and getting it wrong is a regular trap for speakers on 'Thought for the Day' - see this entry.