Somehow I got it into my head that each of the paired 8 clues remained in its own half, and this held me up for ages with apparent clashes all over the place - even though I got the duo, quotation and how the real clash worked. It was only after a bottle of nice Italian wine I realised my mistake.
Not my favourite theme (to put it politely) but a clever puzzle from a setter one can bank on to play fair. I think I'll start reading preambles properly from now on...