You can't really have it both ways - either it's mandatory in which case you'll get London London or it's not in which case you rely on customers putting it their county. In any case the Post Office now no longer require or use counties. We mainly use DHL (where counties are mandatory) and we occasionally have to manually enter counties for people who leave out the county on the website (which does wonders for our geography knowledge) but that's a small price compared with the naff business of London London.

Far more irritating is the business of company name ahead of the individual's name on address labels - but that's just betraying my age!