It turns out the answer was hiding in plain sight. The properties above are a draft proposal at the moment and unsupported by anything I tried. It’s probably a good bet to include them in your calendar for the future – but for it to work now as well, do it like this:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//My Company//NONSGML Event Calendar//EN
URL:http://my.calendar/url
NAME:My Calendar Name
X-WR-CALNAME:My Calendar Name
DESCRIPTION:A description of my calendar
X-WR-CALDESC:A description of my calendar
TIMEZONE-ID:Europe/London
X-WR-TIMEZONE:Europe/London
REFRESH-INTERVAL;VALUE=DURATION:PT12H
X-PUBLISHED-TTL:PT12H
COLOR:34:50:105
CALSCALE:GREGORIAN
METHOD:PUBLISH
The actual working properties at the moment being:
X-WR-CALNAME
X-WR-CALDESC
X-WR-TIMEZONE
X-PUBLISHED-TTL