Once again thanks for letting me know about these changes as I definitely would have been standing around for over an hour otherwise. I wonder how many people will get caught out on Sunday. For some reason I've found it difficult to locate the new Sunday timetable online but picked up a paper copy from the Bus Information Office:
For anyone planning a bus trip to Avebury on Sunday, here are the times -
From Swindon Bus Station: 08.15, 10.15, 12.15, 14.15, 16.15, 18.15
Return from Avebury: 09.34, 11.34, 13.34, 15.34, 17.34, 19.34 (leaving Devizes at 11 minutes past the hour).

I'll put these times under the News Section as well.