I think that you are thinking of the Avro 707, which was an aerodynamic prototype, the 698 was the designation given to the Vulcan.
Unfortunately for my purposes (although fortunately for those involved) the 707 didn't suffer departures from controlled flight of quite the nature I'm trying to research.
I do wonder if the Dh108 might have done, but information on the detail of that accident is incredibly sketchy - and probably was at the time.
G