The issue was with dbus, I had to change the file /etc/dbus-1/system-local.conf to
<policy user="root">
<allow own="org.freedesktop.ReserveDevice1.Audio1"/>
</policy>
Because even though it was the only card it insists on being card1 not card0.
Also the mixer doesn’t appear in the webconf, I presume that’s more to do with the fact you have to launch alsamixer -c1 to view it.
Edit to note: It worked before so it must have been card0 at some point.