Thanks Rob,
Have now got the trim on the car so can't photo.
When I took the trim off previously I was able to pull it off lengthways - pulling from the front of the car - but that was because there was only a couple of clips remaining.
Naively I thought it would go back on the same way but having pop rivetted the new clips - and put them on pointing alternatively left & right - I found quickly that it wouldn't work that way!
So, with them all pointing the same way I found that yes, the way you described it was the way to go. Its not going to come off in the wind, but it is still a little bit loose and I wonder if it might rattle a bit. However with all the other mechanical and wind noises I'm sure that'll be the least of my worries!
Having now twigged how it fits I'm sure I can manage to tweak it better should I have to take it off in future. The paint isn't that great anyway.
Andy