Thanks for the info AgX, very useful.
That's just it.... I've not been using any technique, after a lonnnnng break not doing any film developing. I've been stand developing which, although it has given me good results, isn't quite as good as I want (I think).
As it happens, the ancient Panatomic X was the only "normal" film I have done recently - developed this one using HC110 Dil B for just over 6 mins at 18C, 30 seconds intial and 5 seconds every minute thereafter. Stunning negatives (no fog) from a film expired in October 1970.
Anyway, I had been planning to do NP22 in 1:80 Orwo R09 for 18 mins, and the above agitation - 30 seconds initial, but once every 2 mins thereafter. Sounds like it will be OK.
Thanks again for the info!