I've emailed Tesco about re-using jars as glasses:

Hello,

In France, jars of chocolate spread, mustard etc, are often designed so that you can re-use them as drinking-glasses when the contents are used up.

This seems like a good idea, so I was wondering why we don't take this approach in the UK? Perhaps jars are more expensive to manufacture if they are designed to be re-used.

I plan to publish this enquiry, and your response, on my blog. Let me know if that isn't okay with you.

Thanks for your help with this query,

Tony.

I sent this on 16th August, no reply yet...