SkyDemon - Thanks for the advice
Re the recent comments about SkyDemon - I've only just discovered that it is essentially a NATS-commissioned product. The lite/free version looks good enough for me for the time being (input of routes is simple, and instant access to NOTAMS etc is a great aid all on its own), and a bit of experience with that will tell me if I want to bother with Flight Planning software at all.
At the moment, I suspect the answer will be yes, so I aim to make a final decision just before Christmas . . . . !