Seems no one answered my query on this site (as opposed to http://forums.swedespeed.com/), but I will post the answer. It was the ignition switch. Bought a wrecking yard one, followed the video instructions on how to replace (see https://forums.swedespeed.com/showthread.php?627149-V50-key-will-not-c...

Thanks to Covid, I've not driven my 2007 V50 in a month or so. It has been left outside on the street. When I got to it today, the key fob button for the electric door lock opened fine. Inserted key, all the lights came on as normal, turned key - "key error" came on twice. I have never see...