"You can name the LR part dealer as you're not saying anything about their products that wasn't true - in your opinion of course."
Yes, precisely why I've not named them! They were adamant the problem was at my end, I was adamant it wasn't! I'd rather not got involved in a slanging match with anyone. To be honest they were very helpful over the matter, paying for postage both ways on three sets to ensure I was satisfied, so that's pretty good service. Just a shame the springs were hopeless! Poor product, good retailer, whom I've used for loads of other stuff and had sterling service from.
It was a retailer who uses a green and red colour scheme on their website. Should narrow it down.
I was recommended them by a friend who'd bought their springs and was happy with them (and who helped me install the scary ones) and even he was surprised by the way my van handled.
I've no idea what size a 'batch' of springs is so it may be this was a dodgy run that was sold out and the problem rectified in the next run.
Edit to add: the other 'variables' in the equation, the bushes, were fine, and the shocks also - they were new Bilsteins. The new shocks with the old springs was safe and handled perfectly, although too hard - the reason why I was swapping springs (it had HD rears when I bought it because it was an ex-utility truck and set up for towing a trailer.) The 'new' springs with the Bilsteins were terrible.