Go to Google Calendar (https://calendar.google.com) and sign in.
Find Other Calendars located on the left of the screen, about half way down.
Press on the little down arrow just beside it on the right.
Choose Add by URL
Enter the timetable URL: http://calendar.nexus.ox.ac.uk/owa/calendar/mpptimetable@bsg.ox.ac.uk/Calendar/calendar.ics