They did fit a genuine one, although price wise they're a lot more expensive than aftermarket.

When I had the suspension error message it turned out to be a low battery voltage causing it (thankfully). A full re-charge on trickle overnight cured it.

As others have said the suspension turret wiring is the Adaptive Dynamics fault

Should the suspension make any form of hissing noise under normal operation? I have had the 30mph fault, seemingly triggered at quicker speeds, and had a journey that was less than a mile thankfully, on the bump stops. It cleared when I switched the car off and on again. I was grateful to see this topic at the top of the list! One of my front struts makes a loud hissing and the car wont go up to off-road height so I was thinking split bag? 2012 Westminster Aintree/Ivory 4.4TDV8

Yep, you’ve got a split bag.

Figured as much. Thank you for confirming. I’m going to look at the date on the shock but I think they may be original and will therefore be past their best. There was no suspension work showing in the history.
I’m assuming best to replace both sides at the same time?
OEM the best/only option?
Finally, who is flavour of the month for ordering parts? I think I read that AF have removed the discount code and are operating some kind of reward model. Open to suggestions. 2012 Westminster Aintree/Ivory 4.4TDV8