Google Calendar will not WorK or sync with Calendar.app after Yosemite or IOS 8.1.2 Just in last 3 weeks:-  

Have new computer 3 weeks ago, Yosemite. Had trouble with ical. Would open and load. After perhaps an update, realised the CPU was working hard, fan working hard, activity monitor put iCal 100% CPU usage. Have tried (with Apple support) correcting the library, ical plist; reinstalling software; apple then replaced the new computer. Enabled, disabled, deleted, installed gmail 'internet accounts' on all devices. Cannot deactivate on the phone as it crashes, can't even turn calendar off on the phone setting.

I got replacement computer. Clearly, Not a hardware problem as happening with new computer. 

New Computer, 3 days ago and have now spent Spent 4.5 hours last night with iMac and then iPhone apple support again (1.5 week before). Apple remotely connected to the new computer, took stats and usage info activity monitor while running ical with google calendars.

We determined iCal is working with iCloud.Can create appointments both ways and shows on different devices of different software and OS.
Google Calendar is working with iCal and with Mavericks fine.
Google calendar DOES NOT WORK Yosemite and IOS 8.1.2

ical and Google calendar are NOT working with Yosemite and with new iOS for iPhone and heard iPad.

I had also updated my iPhone few days ago. Noticed the timezone had changed on the calendar appointments. After working with Apple support last night, suggesting restoring phone to earlier back up when it worked. I did a restore last night, but still have the version 8.1.2. Big issues. Can't turn off google calendar. it freezes completely (when trying to turn off calendar). Calendar is blank then crashes.  

So iCal on mac PC does not sync, if it loads, it is causing huge issues and is crashing.
Google calendar doesn't even load on the iPhone. It is crashing.

Apple are working on it their end. Have said it is not an Apple issue, have suggested it
more likely a Google, Calendar issue.
I was having the problem where a couple of events on Google Calendar simply did not show up on Mac Calendar.  I went into the event on Google Calendar and edited it - say, I changed the title slightly.  This somehow "flushed" the event through and it showed up in Mac Calendar.

I noticed this problem arose after I decided to re-link my Google account to my Mac since I was having issues with certain contacts not showing up when I wanted to compose a message in Mac Mail.  Per Google's instructions I re-introduced the Google account as a CardDAV account instead of simply as a Google account.  Not sure this has fixed the contacts problem but it did create the problem above with Calendar sync.

So for me editing the event in question fixed the problem.  But for the bigger problem described by @Michelle Wedd I do not necessarily have an answer.  Maybe she can provide an answer if she has been able to fix the problem.