Further to the Charle's proxy file, where everything seems to stop after authentication, this is what appears on the Mac console:
20/12/13 08:43:44,895 Calendar[12965]: [com.apple.calendar.ui.log] [An error exists on principal: [mpn]]
20/12/13 08:43:45,224 CalendarAgent[202]: -[IAGoogleAuthTokenManager tokenForAccountWithEmailAddress:shouldCreateToken:] [91] -- *** emailAddress is nil, returning nil.
20/12/13 08:43:45,750 CalendarAgent[202]: [com.apple.calendar.store.log.caldav.queue] [CalDAVAccountRefreshQueueableOperation :: calendar home path is empty, not refreshing calendars]
20/12/13 08:43:45,751 CalendarAgent[202]: [com.apple.calendar.store.log.caldav.queue] [Got error on refresh, but not rectifying principal because it was manually configured: Error Domain=CalCalDAVErrorDomain Code=5 "The operation couldn’t be completed. (CalCalDAVErrorDomain error 5.)"]
20/12/13 08:43:45,755 CalendarAgent[202]: [com.apple.calendar.store.log.caldav.queue] [Account refresh failed with error: Error Domain=CalCalDAVErrorDomain Code=5 "The operation couldn’t be completed. (CalCalDAVErrorDomain error 5.)" UserInfo=0x7fc9762a3fc0 {AccountName=mpn, CalDAVErrFromRefresh=YES}]
20/12/13 08:43:45,757 CalendarAgent[202]: [com.apple.calendar.store.log.caldav.queue] [Adding [<CalDAVAccountRefreshQueueableOperation: 0x7fc973fa7540; Sequence: 0>] to failed operations.]