200+ views and no-one expressing an opinion? usually a development query raises a deluge of replies!
It's not the camera as a second roll through a different camera shows identical lines.
So ... it's either my processing, the developer or the film, in that order of likelihood I guess.
I also posted this in Flickr "I shoot film" where replies suggested it is due to over-agitation, and sent a copy to the supplier (Silverprint).
Silverprint forwarded it to Foma, from whom I received a nice email this morning requesting me to send them samples by post.
Now I don't at all mind if the answer comes back "It's your bad technique and crappy developer", but it is really gratifying to have a response like this from the manufacturer.
So, thumbs up for Foma