I'm looking into this for Mrs. Courtman, who is learning at the moment. Like you Wolfie, she is hitting time constraints with work etc. and is also progressing well with the PPL syllabus.
The FAA PPL includes night training as standard I believe, and I think its a good thing - it gives you a bit of experience with instruments and also removes the element of needing to get back to base before the sun goes down (despite proper planning sometimes things can go wrong!).
I still can't find the JAR-FCL syllabus on the net anywhere, and can't find definitive proof that this is permitted. I'm going to call the CAA on Monday, but if anyone can point me in the direction of concrete evidence I'd be grateful! I'll post the outcome of my query to FCLD here when I know it...