Well, apparently "lost in the post" translates as "lost and forgotten about in a pile on some CAA desk". (Or "pending" as they put it.)
Anyway...apparently every flight of a course
should be signed by the instructor
, but this is often let go if the rest of the application is OK. The thing is I'd also entered a date of a partial pass, rather than the re-test pass, and they couldn't accept both these errors. (Legal document and all that).
Thankfully they've reconsidered the application due to the "pending" and have sent the license out this morning. Phew!
Thanks for advice and discussion.