So I thought this was challenging and very enjoyable apart from the undefined letter, which is a pretty fundamental flaw in the whole thing.
As seems to have been the case for several others, the last thing I solved was the first clue, and spent a lot of time looking around that letter as I assumed it wouldnt be possible to have a letter completely undefined like that. Especially as the only answer that fits is somewhat dodgy.
Very enjoyable and all workable through other than that. Shame about that pretty fundamental flaw IMV.